Silence, Sir!

The Sir proteins can silence transcription in yeast at a number of loci, including the mating-type locus, telomeres, and rDNA genes. In an Advanced Online Publication in Nature Genetics, Alo Ray and colleagues at the Cleveland Clinic Foundation, Ohio, US, describe the importance of phosphorylation of Sir3p (Nature Genetics, DOI:10.1038/ng1132, 17 March, 2003).

In a screen for genes affecting silencing loci, Ray et al. identified the Slt2p enzyme as a kinase that phosphorylates Sir3p. Sir3p phosphorylation led to silencing control and reduced lifespan. Conversely, mutation of serine residues in Sir3p extended yeast lifespan by upto 38%. The affects on lifespan occurred independently from changes in rDNA recombination.