期刊
MOLECULAR AND CELLULAR BIOLOGY
卷 25, 期 10, 页码 4299-4310出版社
AMER SOC MICROBIOLOGY
DOI: 10.1128/MCB.25.10.4299-4310.2005
关键词
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The 2 mu m circle plasmid confers no phenotype in wild-type Saccharomyces cerevisiae but in a nib1 mutant, an elevated plasmid copy number is associated with cell death. Complementation was used to identify nib1 as a mutant allele of the ULP1 gene that encodes a protease required for removal of a ubiquitin-like protein, Smt3/SUMO, from protein substrates. The nib1 mutation replaces conserved tryptophan 490 with leucine in the protease domain of Ulp1. Complete deletion of ULP1 is lethal, even in a strain that lacks the 2 mu m circle. Partial deletion of ULP1, like the nib1 mutation, results in clonal variations in plasmid copy number. In addition, a subset of these mutant cells produces lineages in which all cells have reduced proliferative capacity, and this phenotype is dependent upon the presence of the 2 mu m circle. Segregation of the 2 mu m circle requires two plasmid-encoded proteins, Rep1 and Rep2, which were found to colocalize with Ulp1 protein in the nucleus and interact with Smt3 in a two-hybrid assay. These associations and the observation of missegregation of a fluorescently tagged 2 mu m circle reporter plasmid in a subset of ulp1 mutant cells suggest that Smt3 modification plays a role in both plasmid copy number control and segregation.
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