Novel essential DNA repair proteins Nse1 and Nse2 are subunits of the fission yeast Smc5-Smc6 complex.
ABSTRACT The structural maintenance of chromosomes (SMC) family of proteins play essential roles in genomic stability. SMC heterodimers are required for sister-chromatid cohesion (Cohesin: Smc1 & Smc3), chromatin condensation (Condensin: Smc2 & Smc4), and DNA repair (Smc5 & Smc6). The SMC heterodimers do not function alone and must associate with essential non-SMC subunits. To gain further insight into the essential and DNA repair roles of the Smc5-6 complex, we have purified fission yeast Smc5 and identified by mass spectrometry the co-precipitating proteins, Nse1 and Nse2. We show that both Nse1 and Nse2 interact with Smc5 in vivo, as part of the Smc5-6 complex. Nse1 and Nse2 are essential proteins and conserved from yeast to man. Loss of Nse1 and Nse2 function leads to strikingly similar terminal phenotypes to those observed for Smc5-6 inactivation. In addition, cells expressing hypomorphic alleles of Nse1 and Nse2 are, like Smc5-6 mutants, hypersensitive to DNA damage. Epistasis analysis suggests that like Smc5-6, Nse1, and Nse2 function together with Rhp51 in the homologous recombination repair of DNA double strand breaks. The results of this study strongly suggest that Nse1 and Nse2 are novel non-SMC subunits of the fission yeast Smc5-6 DNA repair complex.
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ABSTRACT: Repairing broken chromosomes via joint molecule (JM) intermediates is hazardous and therefore strictly controlled in most organisms. Also in budding yeast meiosis, where production of enough crossovers via JMs is imperative, only a subset of DNA breaks are repaired via JMs, closely regulated by the ZMM pathway. The other breaks are repaired to non-crossovers, avoiding JM formation, through pathways that require the BLM/Sgs1 helicase. "Rogue" JMs that escape the ZMM pathway and BLM/Sgs1 are eliminated before metaphase by resolvases like Mus81-Mms4 to prevent chromosome nondisjunction. Here, we report the requirement of Smc5/6-Mms21 for antagonizing rogue JMs via two mechanisms; destabilizing early intermediates and resolving JMs. Elimination of the Mms21 SUMO E3-ligase domain leads to transient JM accumulation, depending on Mus81-Mms4 for resolution. Absence of Smc6 leads to persistent rogue JMs accumulation, preventing chromatin separation. We propose that the Smc5/6-Mms21 complex antagonizes toxic JMs by coordinating helicases and resolvases at D-Loops and HJs, respectively.PLoS Genetics 12/2013; 9(12):e1004067. · 8.52 Impact Factor
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ABSTRACT: Mesenchymal stem cells (MSC) are progenitor cells that are capable of differentiating into mesenchymal tissues. Fetal and adult MSC have similar morphology but differ in proliferative, differentiating and immunosuppressive properties. Further exploring their differences could help in choosing the right source for cellular therapy. The gene expression profiles of undifferentiated MSC derived from first trimester fetal liver and adult bone marrow were compared by serial analysis of gene expression, and validated by either reverse transcription polymerase chain reaction or immunoblotting of selected genes. The immunophenotype was compared by flow cytometry and cell ELISA. Seventy genes were differentially induced two-fold or more in fetal MSC compared to adult MSC. These involved transcripts regulating germ plasm and limb patterning, brain and early muscle development. Transcripts implicated in cell cycle promotion, chromatin regulation and DNA repair were also more abundant in fetal MSC. Ninety-seven genes were decreased two-fold or more in fetal MSC, including transcripts involved in smooth muscle and keratinocyte differentiation and transcripts for immunological genes. Although phenotypically largely similar, fetal MSC had a higher expression of ICAM1 and contained intracellular deposits of HLA-G while expression of HLA class I and II molecules and VCAM1 was increased in adult MSC. This study reports the first extensive investigation of the differences in gene expression profiles between fetal and adult MSC. The results suggest that fetal MSC have higher proliferative capacity and are less lineage committed than adult MSC.Haematologica 09/2005; 90(8):1017-26. · 5.94 Impact Factor
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ABSTRACT: As a baton in a relay race, intact genomes need to be smoothly passed onto daughter cells every cell generation. Cohesin and condensin are multiprotein complexes involved in chromosome segregation during mitosis, they perform the crucial function of organizing and compacting chromosomes into pairs to facilitate their equal distribution in anaphase. Both complexes share a core of similar origin, containing a heterodimer formed by members of the conserved chromosomal ATPase family named Smc. A third complex containing Smc proteins at its core, the Smc5-Smc6 complex, previously known to be involved in DNA repair has recently been shown to contribute to chromosome segregation during anaphase. Smc5-Smc6 plays a role in the disjunction of repetitive regions. Here, we present results further supporting the importance of Smc5-Smc6 in maintaining the integrity of the repetitive ribosomal DNA (rDNA) locus, the largest repetitive region of the budding yeast genome.Cell cycle (Georgetown, Tex.) 08/2005; 4(7):868-72. · 5.24 Impact Factor