DESCRIPTION (Verbatim from the applicant's abstract): Several different types of DNA elements in eukaryotic nuclei cause regional negative regulation of gene transcription, known as "silencing." Among the best studied examples of silencing occur near telomeres and silent mating type loci in the budding yeast, Saccharomyces cerevisiae, but many additional examples of silencers have been identified in metazoans. This lab previously noted a third form of silencing in yeast. Transcription by RNA polymerase II is antagonized both upstream and downstream of tRNA genes. This inhibition, termed "tRNA gene-mediated (tgm) silencing," requires active transcription of the tRNA gene and does not arise from direct steric occlusion of nearby transcription factor binding. The extent of tgm silencing and the conditions under which it occurs are variable, depending on the pol II promoter. This ability of some pol ll promoters to selectively overcome the silencing effects suggest that tgm silencing is fundamentally different from other forms of silencing in yeast, and that it serves a regulatory function in at least some cases. These effects could influence a large number of loci, since large numbers of tRNA-class promoters are dispersed in throughout the genomes of most eukaryotes. The aims of this project are to investigate the mechanism of conditional tgm silencing in yeast.