In addition to gene specific mechanisms of regulation, gene expression is known to be modulated by more global changes in chromsomal structure as evidenced by such phenomenon as position effect variegation, imprinting, and silencing. Silencing of telomeric gene expression and of the HML and HMR mating type loci in S. cerevisiae represents one of the best defined systems in which this phenomenon has been studied. Work from several laboratories has resulted in the identification of a number of the critical components of this system, including RAP1, SIR1-4, RIF1, and histones H3 and H4. The cis acting sequences at the E mating type silencer are the A, E, and B domains. These bind different trans-acting factors: the ORC replication complex, RAP1 a protein which has been identified as a context dependent repressor or activator, and ABF (ARS binding factor), respectively. Silencing requires two of three of these domains and the aforementioned transacting factors. Of the identified factors, RAP1 is the only one with DNA binding activity. It has been shown to interact with SIR3 and its role is presumed to involve docking other proteins to the DNA. The Shore lab recently showed that SIR1 if targeted to the DNA by a heterologous fusion domain bypassed the requirement for RAP1. Silencing propagated inward from the telomeres and requires the same factors with the exception of SIR1 and is less stable. This grant is highly focused on defining the initiating signals for silencing and on understanding the interactions among the requisite protein factors. There are three specific aims: 1) Characterization of the protein-protein interactions between RAP1 and SIR3 and SIR4; 2) studying the interactions between pairs of SIR proteins in order to identify functional domains involved in initiation and propagation of repressed chromatin; and 3) definition of the molecular role of SIR1 in the establishment of silencing at HM loci.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Genetics Study Section (GEN)
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Columbia University (N.Y.)
Schools of Medicine
New York
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Moretti, P; Shore, D (2001) Multiple interactions in Sir protein recruitment by Rap1p at silencers and telomeres in yeast. Mol Cell Biol 21:8082-94
Vannier, D; Damay, P; Shore, D (2001) A role for Sds3p, a component of the Rpd3p/Sin3p deacetylase complex, in maintaining cellular integrity in Saccharomyces cerevisiae. Mol Genet Genomics 265:560-8
Marcand, S; Wotton, D; Gilson, E et al. (1997) Rap1p and telomere length regulation in yeast. Ciba Found Symp 211:76-93; discussion 93-103
Marcand, S; Gilson, E; Shore, D (1997) A protein-counting mechanism for telomere length regulation in yeast. Science 275:986-90
Shore, D (1997) Telomere length regulation: getting the measure of chromosome ends. Biol Chem 378:591-7
Wotton, D; Shore, D (1997) A novel Rap1p-interacting factor, Rif2p, cooperates with Rif1p to regulate telomere length in Saccharomyces cerevisiae. Genes Dev 11:748-60
Shore, D (1997) Telomerase and telomere-binding proteins: controlling the endgame. Trends Biochem Sci 22:233-5
Marcand, S; Buck, S W; Moretti, P et al. (1996) Silencing of genes at nontelomeric sites in yeast is controlled by sequestration of silencing factors at telomeres by Rap 1 protein. Genes Dev 10:1297-309
Chi, M H; Shore, D (1996) SUM1-1, a dominant suppressor of SIR mutations in Saccharomyces cerevisiae, increases transcriptional silencing at telomeres and HM mating-type loci and decreases chromosome stability. Mol Cell Biol 16:4281-94
Wotton, D; Freeman, K; Shore, D (1996) Multimerization of Hsp42p, a novel heat shock protein of Saccharomyces cerevisiae, is dependent on a conserved carboxyl-terminal sequence. J Biol Chem 271:2717-23

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