REDISTRIBUTION OF SILENCING PROTEINS FROM TELOMERES TO THE NUCLEOLUS IS ASSOCIATED WITH EXTENSION OF LIFE-SPAN IN SACCHAROMYCES-CEREVISIAE

A prior genetic study indicated that activity of Sir silencing protein s at a hypothetical AGE locus is essential for long life span. In this model, the SIR4-42 mutation would direct the Sir protein complex to t he AGE locus, giving rise to a long life span. We show by indirect imm unofluorescence that Sir3p and Sir4p are redirected to the nucleolus i n the SIR4-42 mutant. Furthermore, this relocalization is dependent on both UTH4 a novel yeast gene that extends life span, and its homologu e YGL023. Strikingly, the Sir complex is relocalized from telomeres to the nucleolus in old wild-type cells. We propose that the rDNA is the AGE locus and that nucleolar function is compromised in old yeast cel ls in a way that may be mitigated by targeting of Sir proteins to the nucleolus.