Abstract #37

Silent chromatin and the cohesion of sister chromatids. Marc R. Gartenberg, Ching-Shyi Wu, Rudra Dubey. Pharmacology Dept, Robert Wood Johnson Med School, Piscataway, NJ.
   DNA replication produces sister chromatids that are linked to one another until mitosis by cohesin, a ring shaped complex that is thought to encircle chromatin. At centromeres, cohesin facilitates proper attachment of kinetochores to the mitotic spindle. The complex also binds at other genomic landmarks, including the rDNA array, doubles strand breaks, and sites where transcribing genes converge. We recently found cohesin at the transcriptionally repressed HMR mating-type cassette. Binding and function of cohesin at HMR required the both the Sir proteins and silencers, implicating a critical role for silent chromatin in cohesin targeting. However, it was not clear whether the Sir proteins recruited cohesin directly or whether they suppressed an activity that would otherwise remove cohesin. Here we report on both cis and trans acting factors that are necessary and sufficient for recruitment of cohesin to HMR. The roles of Sir2 and the tRNA gene at the heterochromatin boundary will be discussed.

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