Abstract
The Saccharomyces cerevisiase protein phosphatase Fcp1 has been implicated in the regulation of transcription by RNA polymerase II, and is encoded by the essential gene FCP1. A screen was carried out for multicopy suppressors of the temperature-sensitive phenotype of two phosphatase mutants, fcp1-2 and fcp1-4. Only the wild-type FCP1 was found to suppress (complement) the fcp1-4 mutation. For fcp1-2 three second-site suppressors were identified. One contained the ORF for ZDS1. The remaining two suppressors mapped to the centromere regions of chromosomes I and V. Suppression due to centromere DNA was found to be more dependent on the CDEIII region than on other regions of the centromere. The presence of a suppressor centromere affected the level of Fcp1 protein and the overall phosphorylation state of RNA polymerase II (RNAPII) in fcp1-2 cells, but not wild-type cells, grown at both permissive and non-permissive temperatures. In addition, genetic interactions were identified between this FCP1 mutant and the genes SKP1, CEP3 and CBF1, which code for centromere binding proteins. The mechanism of suppression and regulation of Fcp1-2 protein activity by centromeric DNA is discussed.
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