Mcm10 plays a direct role in transcriptional silencing in Saccharomyces cerevisiae.
Ivan Liachko, Nancy L. Douglas, Bik K. Tye
Molecular Biology and Genetics, Cornell University, 327 Biotech Bldg, Ithaca, NY, 14853, USA
Mcm10 is an essential DNA replication protein which interacts with several components of replication machinery. Here we present a role for Mcm10 in heterochromatic silencing at budding yeast telomeres and HM loci. Two mcm10 mutants drastically reduce silencing of both URA3 and ADE2 reporter genes integrated into silent loci. When exposed to alpha-factor, mcm10 mutant MATa cells display a 'shmoo-cluster' phenotype associated with a defect in the maintenance of HML silencing. In addition, when combined with a defect in the establishment of silent chromatin (conferred by a sir1 deletion), mcm10 mutants demonstrate a synergistic defect in HML silencing. Consistent with a direct silencing function, Mcm10 shows a two-hybrid interaction with Sir2 and Sir3. Tethering GBD-MCM10 to a defective HMR-E silencer is not sufficient to restore silencing. However, mutations in MCM10 inhibit the ability of GBD-SIR3 to restore silencing when tethered to a defective HMR-E. We isolated two mutants in another gene, MCM2, which are able to suppress the temperature-sensitivity of mcm10-1 mutants. Surprisingly, these suppressor mutations are not able to overcome the mcm10-1 silencing defect, suggesting that MCM10's role in transcriptional silencing is separate from its essential functions in DNA replication.
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