SET1, A YEAST MEMBER OF THE TRITHORAX FAMILY, FUNCTIONS IN TRANSCRIPTIONAL SILENCING AND DIVERSE CELLULAR PROCESSES

The trithorax gene family contains members implicated in the control o f transcription, development, chromosome structure, and human leukemia . A feature shared by some family members, and by other proteins that function in chromatin-mediated transcriptional regulation, is the pres ence of a 130- to 140-amino acid motif dubbed the SET or Tromo domain. Here we present analysis of SET1, a yeast member of the trithorax gen e family that was identified by sequence inspection to encode a 1080-a mino acid protein with a C-terminal SET domain. In addition to its SET domain, which is 40-50% identical to those previously characterized, SET1 also shares dispersed but significant similarity to Drosophila an d human trithorax homologues. To understand SET1 function(s), we creat ed a null mutant. Mutant strains, although viable, are defective in tr anscriptional silencing of the silent mating-type loci and telomeres. The telomeric silencing defect is rescued not only by full-length epis omal SET1 but also by the conserved SET domain of SET1. set1 mutant st rains display other phenotypes including morphological abnormalities, stationary phase defects, and growth and sporulation defects. Candidat e genes that may interact with SET1 include those with functions in tr anscription, growth, and cell cycle control. These data suggest that y east SET1, like its SET domain counterparts in other organisms, functi ons in diverse biological processes including transcription and chroma tin structure.