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Super-resolution imaging of the structural maintenance of chromosome (SMC) complexes cohesin and condensin

Almada, Pedro Manuel Bento Carvalho, 1986-
Fonte: Universidade de Lisboa Publicador: Universidade de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2013 ENG
Relevância na Pesquisa
27.15%
Tese de mestrado. Biologia (Biologia Celular e Biotecnologia). Universidade de Lisboa, Faculdade de Ciências, 2013; Os complexos proteicos “Structural Maintenance of Chromosomes” (SMC) têm papéis importantes na estrutura cromossómica. Destes, destacam-se a coesina e as condensinas. A coesina mantém os cromatídeos irmãos unidos de modo a permitir a sua fiel segregação enquanto que as condensinas são principalmente responsáveis pela condensação dos cromossomas em preparação para a divisão celular1. A distribuição destes complexos no cromossoma e a sua interacção com outras proteínas associadas ao ADN é actualmente alvo de intensa investigação. Quando os cromossomas estão condensados sabe-se que a condensina aparece num eixo restrito ao longo dos cromatídeos. Sabe-se também que neste período as coesinas estão localizadas maioritariamente na região pericentromérica. Mas não é ainda conhecido se a sua distribuição abrange toda a largura da do centrómero ou, para os dois complexos, se têm uma distribuição restrita centralmente, se pontual ou difusa (figura 3). O limite para perceber a sua distribuição é resultado do limite de resolução das técnicas tradicionais de microscopia óptica. Estas estão limitadas pela difracção da luz a uma resolução de cerca de 200 nm. Embora a microscopia electrónica consiga maior resolução...

The Caulobacter crescentus smc gene is required for cell cycle progression and chromosome segregation

Jensen, Rasmus B.; Shapiro, Lucy
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 14/09/1999 EN
Relevância na Pesquisa
27.15%
The highly conserved SMC (Structural Maintenance of Chromosomes) proteins function in chromosome condensation, segregation, and other aspects of chromosome dynamics in both eukaryotes and prokaryotes. A null mutation in the Caulobacter crescentus smc gene is conditionally lethal and causes a cell cycle arrest at the predivisional cell stage. Chromosome segregation in wild-type and smc null mutant cells was examined by monitoring the intracellular localization of the replication origin and terminus by using fluorescence in situ hybridization. In wild-type cells, the origin is located at the flagellated pole of swarmer cells and, immediately after the initiation of DNA replication in stalked cells, one of the origins moves to the opposite pole, giving a bipolar localization of the origins. The terminus moves from the end of the swarmer cell opposite the origin to midcell. A subpopulation of the smc null mutant cells had mislocalized origins or termini, showing that the smc null mutation gives DNA segregation defects. Nucleoid morphology was also abnormal. Thus, we propose that the Caulobacter chromosomal origins have specific cellular addresses and that the SMC protein plays important roles in maintaining chromosome structure and in partitioning. The specific cell cycle arrest in the smc null mutant indicates the presence of a cell cycle checkpoint that senses perturbations in chromosome organization or segregation.

Bacillus subtilis SMC Is Required for Proper Arrangement of the Chromosome and for Efficient Segregation of Replication Termini but Not for Bipolar Movement of Newly Duplicated Origin Regions

Graumann, Peter L.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /11/2000 EN
Relevância na Pesquisa
27.23%
SMC protein is required for chromosome condensation and for the faithful segregation of daughter chromosomes in Bacillus subtilis. The visualization of specific sites on the chromosome showed that newly duplicated origin regions in growing cells of an smc mutant were able to segregate from each other but that the location of origin regions was frequently aberrant. In contrast, the segregation of replication termini was impaired in smc mutant cells. This analysis was extended to germinating spores of an smc mutant. The results showed that during germination, newly duplicated origins, but not termini, were able to separate from each other in the absence of SMC. Also, DAPI (4′,6′-diamidino-2-phenylindole) staining revealed that chromosomes in germinating spores were able to undergo partial or complete replication but that the daughter chromosomes were blocked at a late stage in the segregation process. These findings were confirmed by time-lapse microscopy, which showed that after duplication in growing cells the origin regions underwent rapid movement toward opposite poles of the cell in the absence of SMC. This indicates that SMC is not a required component of the mitotic motor that initially drives origins apart after their duplication. It is also concluded that SMC is needed to maintain the proper layout of the chromosome in the cell and that it functions in the cell cycle after origin separation but prior to complete segregation or replication of daughter chromosomes. It is proposed here that chromosome segregation takes place in at least two steps: an SMC-independent step in which origins move apart and a subsequent SMC-dependent step in which newly duplicated chromosomes condense and are thereby drawn apart.

Subcellular Localization of Bacillus subtilis SMC, a Protein Involved in Chromosome Condensation and Segregation

Graumann, Peter L.; Losick, Richard; Strunnikov, Alexander V.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /11/1998 EN
Relevância na Pesquisa
27.21%
We have investigated the subcellular localization of the SMC protein in the gram-positive bacterium Bacillus subtilis. Recent work has shown that SMC is required for chromosome condensation and faithful chromosome segregation during the B. subtilis cell cycle. Using antibodies against SMC and fluorescence microscopy, we have shown that SMC is associated with the chromosome but is also present in discrete foci near the poles of the cell. DNase treatment of permeabilized cells disrupted the association of SMC with the chromosome but not with the polar foci. The use of a truncated smc gene demonstrated that the C-terminal domain of the protein is required for chromosomal binding but not for the formation of polar foci. Regular arrays of SMC-containing foci were still present between nucleoids along the length of aseptate filaments generated by depleting cells of the cell division protein FtsZ, indicating that the formation of polar foci does not require the formation of septal structures. In slowly growing cells, which have only one or two chromosomes, SMC foci were principally observed early in the cell cycle, prior to or coincident with chromosome segregation. Cell cycle-dependent release of stored SMC from polar foci may mediate segregation by condensation of chromosomes.

Cell-Cycle-Regulated Expression and Subcellular Localization of the Caulobacter crescentus SMC Chromosome Structural Protein

Jensen, Rasmus B.; Shapiro, Lucy
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /05/2003 EN
Relevância na Pesquisa
27.23%
Structural maintenance of chromosomes proteins (SMCs) bind to DNA and function to ensure proper chromosome organization in both eukaryotes and bacteria. Caulobacter crescentus possesses a single SMC homolog that plays a role in organizing and segregating daughter chromosomes. Approximately 1,500 to 2,000 SMC molecules are present per cell during active growth, corresponding to one SMC complex per 6,000 to 8,000 bp of chromosomal DNA. Although transcription from the smc promoter is induced during early S phase, a cell cycle transcription pattern previously observed with multiple DNA replication and repair genes, the SMC protein is present throughout the entire cell cycle. Examination of the intracellular location of SMC showed that in swarmer cells, which do not replicate DNA, the protein forms two or three foci. Stalked cells, which are actively engaged in DNA replication, have three or four SMC foci per cell. The SMC foci appear randomly distributed in the cell. Many predivisional cells have bright polar SMC foci, which are lost upon cell division. Thus, chromosome compaction likely involves dynamic aggregates of SMC bound to DNA. The aggregation pattern changes as a function of the cell cycle both during and upon completion of chromosome replication.

Condensin but not cohesin SMC heterodimer induces DNA reannealing through protein–protein assembly

Sakai, Akiko; Hizume, Kohji; Sutani, Takashi; Takeyasu, Kunio; Yanagida, Mitsuhiro
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
Publicado em 02/06/2003 EN
Relevância na Pesquisa
27.23%
Condensin and cohesin are chromosomal protein complexes required for chromosome condensation and sister chromatid cohesion, respectively. They commonly contain the SMC (structural maintenance of chromosomes) subunits consisting of a long coiled-coil with the terminal globular domains and the central hinge. Condensin and cohesin holo-complexes contain three and two non-SMC subunits, respectively. In this study, DNA interaction with cohesin and condensin complexes purified from fission yeast was investigated. The DNA reannealing activity is strong for condensin SMC heterodimer but weak for holo-condensin, whereas no annealing activity is found for cohesin heterodimer SMC and Rad21-bound heterotrimer complexes. One set of globular domains of the same condensin SMC is essential for the DNA reannealing activity. In addition, the coiled-coil and hinge region of another SMC are needed. Atomic force microscopy discloses the molecular events of DNA reannealing. SMC assembly that occurs on reannealing DNA seems to be a necessary intermediary step. SMC is eliminated from the completed double-stranded DNA. The ability of heterodimeric SMC to reanneal DNA may be regulated in vivo possibly through the non-SMC heterotrimeric complex.

Conserved Disruptions in the Predicted Coiled-Coil Domains of Eukaryotic SMC Complexes: Implications for Structure and Function

Beasley, Matthew; Xu, Huiling; Warren, William; McKay, Michael
Fonte: Cold Spring Harbor Laboratory Press Publicador: Cold Spring Harbor Laboratory Press
Tipo: Artigo de Revista Científica
Publicado em /08/2002 EN
Relevância na Pesquisa
27.15%
The structural maintenance of chromosome (SMC) proteins are required for a number of essential nuclear processes, including those of chromosome condensation, chromatid cohesion, and DNA repair. Eukaryotic SMC proteins form heterodimers capable of binding DNA and possess a DNA-stimulated ATPase activity. They have a characteristic structure of terminal globular domains with two internal arms that are predicted to form a coiled-coil structure interspaced with a globular “hinge” domain. We report here that the predicted coiled-coil arms are disrupted at conserved sites in SMC proteins. These disruptions, which vary in length and sequence identity, abolish the otherwise symmetrical secondary structure of antiparallel SMC heterodimers and provide the first evidence for a possible functional orientation of eukaryotic SMC complexes. The retention of these breaks between evolutionarily distant, yet related, SMC members indicates that they may have a fundamental role in SMC heterodimer function.

Genetic Interactions of smc, ftsK, and parB Genes in Streptomyces coelicolor and Their Developmental Genome Segregation Phenotypes▿ †

Dedrick, Rebekah M.; Wildschutte, Hans; McCormick, Joseph R.
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.15%
The mechanisms by which chromosomes condense and segregate during developmentally regulated cell division are of interest for Streptomyces coelicolor, a sporulating, filamentous bacterium with a large, linear genome. These processes coordinately occur as many septa synchronously form in syncytial aerial hyphae such that prespore compartments accurately receive chromosome copies. Our genetic approach analyzed mutants for ftsK, smc, and parB. DNA motor protein FtsK/SpoIIIE coordinates chromosome segregation with septum closure in rod-shaped bacteria. SMC (structural maintenance of chromosomes) participates in condensation and organization of the nucleoid. ParB/Spo0J partitions the origin of replication using a nucleoprotein complex, assembled at a centromere-like sequence. Consistent with previous work, we show that an ftsK-null mutant produces anucleate spores at the same frequency as the wild-type strain (0.8%). We report that the smc and ftsK deletion-insertion mutants (ftsK′ truncation allele) have developmental segregation defects (7% and 15% anucleate spores, respectively). By use of these latter mutants, viable double and triple mutants were isolated in all combinations with a previously described parB-null mutant (12% anucleate spores). parB and smc were in separate segregation pathways; the loss of both exacerbates the segregation defect (24% anucleate spores). For a triple mutant...

SMC Protein-Dependent Chromosome Condensation during Aerial Hyphal Development in Streptomyces▿ †

Kois, Agnieszka; Świątek, Magdalena; Jakimowicz, Dagmara; Zakrzewska-Czerwińska, Jolanta
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.15%
Members of the SMC (structural maintenance of chromosomes) protein family play a central role in higher-order chromosome dynamics from bacteria to humans. So far, studies of bacterial SMC proteins have focused only on unicellular rod-shaped organisms that divide by binary fission. The conversion of multigenomic aerial hyphae of the mycelial organism Streptomyces coelicolor into chains of unigenomic spores requires the synchronous segregation of multiple chromosomes. Here we focus on the contribution of SMC proteins to sporulation-associated chromosome segregation in S. coelicolor. Deletion of the smc gene causes aberrant DNA condensation and missegregation of chromosomes (7.5% anucleate spores). In vegetative mycelium, immunostained SMC proteins were observed sporadically, while in aerial hyphae about to undergo sporulation they appeared as irregularly spaced foci which accompanied but did not colocalize with ParB complexes. Our data demonstrate that efficient chromosome segregation requires the joint action of SMC and ParB proteins. SMC proteins, similarly to ParAB and FtsZ, presumably belong to a larger group of proteins whose expression is highly induced in response to the requirement of aerial hyphal maturation.

Structure and DNA binding activity of the mouse condensin hinge domain highlight common and diverse features of SMC proteins

Griese, Julia J.; Witte, Gregor; Hopfner, Karl-Peter
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.15%
Structural Maintenance of Chromosomes (SMC) proteins are vital for a wide range of processes including chromosome structure and dynamics, gene regulation and DNA repair. Eukaryotes have three SMC complexes, consisting of heterodimeric pairs of six different SMC proteins along with several specific regulatory subunits. In addition to their other functions, all three SMC complexes play distinct roles in DNA repair. Cohesin (SMC1–SMC3) is involved in DNA double-strand break repair, condensin (SMC2–SMC4) participates in single-strand break (SSB) repair, and the SMC5–SMC6 complex functions in various DNA repair pathways. SMC proteins consist of N- and C-terminal domains that fold back onto each other to create an ATPase ‘head’ domain, connected to a central ‘hinge’ domain via long coiled-coils. The hinge domain mediates dimerization of SMC proteins and binds DNA, but it is not clear to what purpose this activity serves. We studied the structure and function of the condensin hinge domain from mouse. While the SMC hinge domain structure is largely conserved from prokaryotes to eukaryotes, its function seems to have diversified throughout the course of evolution. The condensin hinge domain preferentially binds single-stranded DNA. We propose that this activity plays a role in the SSB repair function of the condensin complex.

Using DNA as a Fiducial Marker To Study SMC Complex Interactions with the Atomic Force Microscope

Fuentes-Perez, M.E.; Gwynn, E.J.; Dillingham, M.S.; Moreno-Herrero, F.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 22/02/2012 EN
Relevância na Pesquisa
27.21%
Atomic force microscopy can potentially provide information on protein volumes, shapes, and interactions but is susceptible to variable tip-induced artifacts. In this study, we present an atomic force microscopy approach that can measure volumes of nonglobular polypeptides such as structural maintenance of chromosomes (SMC) proteins, and use it to study the interactions that occur within and between SMC complexes. Together with the protein of interest, we coadsorb a DNA molecule and use it as a fiducial marker to account for tip-induced artifacts that affect both protein and DNA, allowing normalization of protein volumes from images taken on different days and with different tips. This approach significantly reduced the error associated with volume analysis, and allowed determination of the oligomeric states and architecture of the Bacillus subtilis SMC complex, formed by the SMC protein, and by the smaller ScpA and ScpB subunits. This work reveals that SMC and ScpB are dimers and that ScpA is a stable monomer. Moreover, whereas ScpA binds directly to SMC, ScpB only binds to SMC in the presence of ScpA. Notably, the presence of both ScpA and ScpB favored the formation of higher-order structures of SMC complexes, suggesting a role for these subunits in the organization of SMC oligomers.

SMC Condensation Centers in Bacillus subtilis Are Dynamic Structures

Kleine Borgmann, Luise A. K.; Hummel, Hanna; Ulbrich, Maximilian H.; Graumann, Peter L.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /05/2013 EN
Relevância na Pesquisa
27.23%
SMC and MukB complexes consist of a central SMC dimer and two essential binding partners, ScpA and ScpB (MukE and MukF), and are crucial for correct chromosome compaction and segregation. The complexes form two bipolar assemblies on the chromosome, one in each cell half. Using fluorescence recovery after photobleaching (FRAP), we provide evidence that the SMC complex has high exchange rates. This depends to a considerable degree on de novo protein synthesis, revealing that the bacterial SMC complex has high on and off rates for binding to the chromosome. A mutation in SMC that affects ATPase activity and results in exaggerated DNA binding in vitro causes a strong segregation defect in vivo and affects the localization of the entire SMC complex, which localizes to many more sites in the cell than under normal conditions. These data indicate that ATP turnover is important for the function of Bacillus subtilis SMC. In contrast, the centromere protein Spo0J and DNA gyrase showed much less exchange between distinct binding sites on the chromosome than that seen with SMC. Binding of Spo0J to the origin regions was rather static and remained partially conserved until the next cell cycle. Our experiments reveal that the SMC complex has a high...

The SMC condensin complex is required for origin segregation in Bacillus subtilis

Wang, Xindan; Tang, Olive W.; Riley, Eammon P.; Rudner, David Z.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.18%
SMC condensin complexes play a central role in organizing and compacting chromosomes in all domains of life [1, 2]. In the bacterium Bacillus subtilis, cells lacking SMC are viable only during slow growth and display decondensed chromosomes, suggesting that SMC complexes function throughout the genome [3, 4]. Here, we show that rapid inactivation of SMC or its partner protein ScpB during fast growth leads to a failure to resolve newly replicated origins and a complete block to chromosome segregation. Importantly, the loss of origin segregation is not due to an inability to unlink pre-catenated sister chromosomes by Topoisomerase IV. In support of the idea that ParB-mediated recruitment of SMC complexes to the origin is important for their segregation, cells with reduced levels of SMC that lack ParB are severely impaired in origin resolution. Finally, we demonstrate that origin segregation is a task shared by the condensin complex and the parABS partitioning system. We propose that origin-localized SMC constrains adjacent DNA segments along their lengths, drawing replicated origins in on themselves and away from each other. This SMC-mediated lengthwise condensation, bolstered by the parABS system, drives origin segregation.

Molecular Basis for SMC Rod Formation and Its Dissolution upon DNA Binding

Soh, Young-Min; Bürmann, Frank; Shin, Ho-Chul; Oda, Takashi; Jin, Kyeong Sik; Toseland, Christopher P.; Kim, Cheolhee; Lee, Hansol; Kim, Soo Jin; Kong, Min-Seok; Durand-Diebold, Marie-Laure; Kim, Yeon-Gil; Kim, Ho Min; Lee, Nam Ki; Sato, Mamoru; Oh,
Fonte: Cell Press Publicador: Cell Press
Tipo: Artigo de Revista Científica
Publicado em 22/01/2015 EN
Relevância na Pesquisa
27.18%
SMC condensin complexes are central modulators of chromosome superstructure in all branches of life. Their SMC subunits form a long intramolecular coiled coil, which connects a constitutive “hinge” dimerization domain with an ATP-regulated “head” dimerization module. Here, we address the structural arrangement of the long coiled coils in SMC complexes. We unequivocally show that prokaryotic Smc-ScpAB, eukaryotic condensin, and possibly also cohesin form rod-like structures, with their coiled coils being closely juxtaposed and accurately anchored to the hinge. Upon ATP-induced binding of DNA to the hinge, however, Smc switches to a more open configuration. Our data suggest that a long-distance structural transition is transmitted from the Smc head domains to regulate Smc-ScpAB’s association with DNA. These findings uncover a conserved architectural theme in SMC complexes, provide a mechanistic basis for Smc’s dynamic engagement with chromosomes, and offer a molecular explanation for defects in Cornelia de Lange syndrome.

Proliferating or interleukin 1-activated human vascular smooth muscle cells secrete copious interleukin 6

Loppnow, H; Libby, Peter
Fonte: American Society for Clinical Investigation Publicador: American Society for Clinical Investigation
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
27.28%
The cells that make up blood vessel walls appear to participate actively in local immune and inflammatory responses, as well as in certain vascular diseases. We tested here whether smooth muscle cells (SMC) can produce the important inflammatory mediator IL6. Unstimulated SMC in vitro elaborated 5 X 10(3) pg recIL6/24h (i.e., biological activity equivalent to 5 X 10(3) pg recombinant IL6 (recIL6), as determined in B9-assay with a recIL6 standard). Several pathophysiologically relevant factors augmented IL6 release from SMC including 10 micrograms LPS/ml (10(4) pg recIL6), 10 ng tumor necrosis factor/ml (4 X 10(4) pg recIL6), and most notably 10 ng IL1/ml (greater than or equal to 3.2 X 10(5) pg recIL6). Production of IL6 activity corresponded to IL6 mRNA accumulation and de novo synthesis. SMC released newly synthesized IL6 rapidly, as little metabolically labeled material remained cell-associated. In supernatants of IL1-stimulated SMC, IL6 accounted for as much as 4% of the secreted proteins. In normal vessels SMC seldom divide, but SMC proliferation can occur in hypertension or during atherogenesis. We therefore tested the relationship between IL6 production and SMC proliferation in response to platelet-derived growth factor (PDGF) in vitro. Quiescent SMC released scant IL6 activity...

Non Linear Proper Generalized Decomposition method applied to the magnetic simulation of a SMC microstructure

HENNERON, Thomas; BENABOU, Abdelkader; CLENET, Stéphane
Fonte: IEEE Publicador: IEEE
EN
Relevância na Pesquisa
36.9%
Improvement of the magnetic performances of Soft Magnetic Composites (SMC) materials requires to link the microstructures to the macroscopic magnetic behavior law. This can be achieved with the FE method using the geometry reconstruction from images of the microstructure. Nevertheless, it can lead to large computational times. In that context, the Proper Generalized Decomposition (PGD), that is an approximation method originally developed in mechanics, and based on a finite sum of separable functions, can be of interest in our case. In this work, we propose to apply the PGD method to the SMC microstructure magnetic simulation. A non-linear magnetostatic problem with the scalar potential formulation is then solved.

Spectroscopy of MACHO 97-SMC-1: self-lensing within the SMC

Sahu, Kailash C.; Sahu, M. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/10/1998
Relevância na Pesquisa
27.27%
More than a dozen microlensing events have been detected so far towards the LMC and 2 towards the SMC. If all the lenses are in the Galactic halo, both the LMC and the SMC events are expected to have similar time scales. However, the first event towards the SMC, MACHO 97-SMC-1, had a time scale of 123 days which is much larger than the typical time scale for the LMC events. From optical depth estimates, we first show that the stars within the SMC play a dominant role as gravitational lenses and can fully account for the observed microlensing events, mainly due to its large physical depth. We also show that if the lenses are within the Magellanic Clouds, then the SMC events should be longer in duration than the LMC events, a fact that is consistent with the observations. The time scale of the event implies that the mass of the lens is >2 solar masses if it is in the Milky Way disk or halo, in which case the lens is expected to be bright and should reveal itself in the spectrum. Here, we present an optical spectrum of MACHO 97-SMC-1 which shows that the lens is not in the Milky Way disk or halo, but is a low-mass star within the SMC. It is worth noting here that MACHO SMC-98-1 is the only OTHER observed event towards the SMC. This was a binary lens event where the caustic crossing time-scale as observed by PLANET...

Surveying the Agents of Galaxy Evolution in the Tidally-Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC) II. Cool Evolved Stars

Boyer, Martha L.; Srinivasan, Sundar; van Loon, Jacco Th.; McDonald, Iain; Meixner, Margaret; Zaritsky, Dennis; Gordon, Karl D.; Kemper, F.; Babler, Brian; Block, Miwa; Bracker, Steve; Engelbracht, Charles W.; Hora, Joe; Indebetouw, Remy; Meade, Marilyn;
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/06/2011
Relevância na Pesquisa
27.18%
We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled: "Surveying the Agents of Galaxy Evolution in the Tidally-stripped, Low Metallicity SMC", or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at infrared (IR) wavelengths (3.6 - 160 microns). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute ~20% of the global SMC flux (extended + point-source) at 3.6 microns, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies. The equivalent SAGE survey of the higher-metallicity Large Magellanic Cloud (SAGE-LMC) allows us to explore the influence of metallicity on dust production. We find that the SMC RSG stars are less likely to produce a large amount of dust (as indicated by the [3.6]-[8] color). There is a higher fraction of carbon-rich stars in the SMC...

A Quantitative Comparison of SMC, LMC, and Milky Way UV to NIR Extinction Curves

Gordon, Karl D.; Clayton, Geoffrey C.; Misselt, K. A.; Landolt, Arlo U.; Wolff, Michael J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/05/2003
Relevância na Pesquisa
27.18%
We present an exhaustive, quantitative comparison of all of the known extinction curves in the Small and Large Magellanic Clouds (SMC and LMC) with our understanding of the general behavior of Milky Way extinction curves. The R_V dependent CCM relationship and the sample of extinction curves used to derive this relationship is used to describe the general behavior of Milky Way extinction curves. The ultraviolet portion of the SMC and LMC extinction curves are derived from archival IUE data, except for one new SMC extinction curve which was measured using HST/STIS observations. The optical extinction curves are derived from new (for the SMC) and literature UBVRI photometry (for the LMC). The near-infrared extinction curves are calculated mainly from 2MASS photometry supplemented with DENIS and new JHK photometry. For each extinction curve, we give R_V = A(V)/E(B-V) and N(HI) values which probe the same dust column as the extinction curve. We compare the properties of the SMC and LMC extinction curves with the CCM relationship three different ways: each curve by itself, the behavior of extinction at different wavelengths with R_V, and behavior of the extinction curve FM fit parameters with R_V. As has been found previously, we find that a small number of LMC extinction curves are consistent with the CCM relationship...

SMC proteins, new players in the maintenance of genomic stability

Cortés-Ledesma, Felipe; Piccoli, Giaccomo de; Haber, James E.; Aragón, Luis; Aguilera, Andrés
Fonte: Landes Bioscience Publicador: Landes Bioscience
Tipo: Artículo Formato: 21663 bytes; application/pdf
ENG
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PMID: 17404505.-- Previously published online as a Cell Cycle E-publication: http://www.landesbioscience.com/journals/cc/abstract.php?id=4107; Homologous recombination (HR) is one of the key mechanisms responsible for the repair of DNA double-strand breaks (DSBs), including those that occur during DNA replication. Recent studies in yeast and mammals have uncovered that the SMC complexes cohesins and Smc5-Smc6 are recruited to induced DSBs, and play a role in the maintenance of genome stability by favouring SCR as the main recombinational DSB repair mechanism. These new results raise intriguing questions such as whether SMC proteins might play a functional role at collapsed replication forks, which may represent the main source of spontaneous recombinogenic damage. A deeper knowledge of the role of SMC proteins in DSB repair should contribute to a better understanding of chromosome dynamics and stability.; Peer reviewed