ABSTRACT
The cohesin network has an essential role in chromosome segregation, but also plays a role in DNA damage repair. Eco1 is an acetyltransferase that targets subunits of the cohesin complex and is involved in both the chromosome segregation and DNA damage repair roles of the network. Using budding yeast as a model system, we find that mutations in Eco1, including a genocopy of a human Roberts syndrome allele, do not cause gross defects in chromosome cohesion. We examined how mitotic and meiotic DNA damage repair is affected by mutations in Eco1. Strains containing mutations in Eco1 are sensitive to DNA damaging agents that cause double-strand breaks, such as X-rays and bleomycin. While meiotic crossing over is relatively unaffected in strains containing the Roberts mutation, reciprocal mitotic crossovers occur with extremely low frequency in this mutant background. Our results suggest that Eco1 promotes the reciprocal exchange of chromosome arms and maintenance of heterozygosity during mitosis.
Subject(s)
Acetyltransferases/metabolism , DNA Repair , Nuclear Proteins/metabolism , Saccharomyces cerevisiae Proteins/metabolism , Saccharomyces cerevisiae/enzymology , Acetyltransferases/genetics , Antibiotics, Antineoplastic/chemistry , Bleomycin/chemistry , Cell Cycle Proteins/metabolism , Checkpoint Kinase 2 , Chromosomal Proteins, Non-Histone/metabolism , Chromosome Segregation , DNA Breaks, Double-Stranded , Mitosis , Mutation , Nuclear Proteins/genetics , Phosphorylation , Protein Serine-Threonine Kinases/metabolism , Saccharomyces cerevisiae/growth & development , Saccharomyces cerevisiae Proteins/genetics , X-Rays , CohesinsABSTRACT
In Saccharomyces cerevisiae, chromatin is spatially organized within the nucleus with centromeres clustering near the spindle pole body, telomeres clustering into foci at the nuclear periphery, ribosomal DNA repeats localizing within a single nucleolus, and transfer RNA (tRNA) genes present in an adjacent cluster. [corrected] Furthermore, certain genes relocalize from the nuclear interior to the periphery upon transcriptional activation. The molecular mechanisms responsible for the organization of the genome are not well understood. We find that evolutionarily conserved proteins in the cohesin network play an important role in the subnuclear organization of chromatin. Mutations that cause human cohesinopathies had little effect on chromosome cohesion, centromere clustering, or viability when expressed in yeast. However, two mutations in particular lead to defects in (a) GAL2 transcription and recruitment to the nuclear periphery, (b) condensation of mitotic chromosomes, (c) nucleolar morphology, and (d) tRNA gene-mediated silencing and clustering of tRNA genes. We propose that the cohesin network affects gene regulation by facilitating the subnuclear organization of chromatin.
