ROLES OF ABF1, NPL3, AND YCL54 IN SILENCING IN SACCHAROMYCES-CEREVISIAE

A sensitized genetic screen was carried out to identify essential gene s involved in silencing in Saccharomyces cerevisiae. This screen ident ified temperature-sensitive alleles of ORC2 and ORC5, as described els ewhere, and ABF1, NPL3, and YCL54, as described here. Alleles of ABF1 that caused silencing defects provided the genetic proof of Abflp's ro le in silencing. The roles of Np13p and Yc154p are less clear. These p roteins did not act exclusively through any one of the three protein b inding sites of the HMR-E silencer. Unlike the orc2, orc5, and abf1 mu tations that were isolated in the same (or a similar) screen for silen cing mutants, neither temperature-sensitive mutation in NPL3 or YCL54 caused overt replication defects.