Two classes of sir3 mutants enhance the sir1 mutant mating defect and abolish telomeric silencing in Saccharomyces cerevisiae.
Silent information regulators, or Sir proteins, play distinct roles in chromatin-mediated transcriptional control at the silent mating-type loci, telomeres, and within the rDNA repeats of Saccharomyces cerevisiae. An unusual collection of sir3 mutant alleles was identified in a genetic screen for enhancers of the sir1 mutant mating-defective phenotype. These sir3-eso mutants, like the sir1 mutant, exhibit little or no mating defects alone, but the sir1 sir3-eso double mutants are essentially nonmating. All of the sir3-eso mutants are defective in telomeric silencing. In some mutants, this phenotype is suppressed by tethering Sir1p to telomeres; other mutants are dominant for mating and telomeric silencing defects. Additionally, several sir3-eso mutants are nonmating in combination with the nat1 N-terminal acetyltransferase mutant. The temperature-sensitive allele sir3-8 has an eso phenotype at permissive temperature, yet acts as a null allele at restrictive temperature due to loss of sir3-8 protein. Sequence analysis showed that eight of the nine sir3-eso alleles have mutations within the N-terminal region that is highly similar to the DNA replication initiation protein Orc1p. Together, these data reveal modular domains for Sir3p and further define its function in silencing chromatin.
Stone
E M
EM
Department of Biology, University of California, San Diego 92093-0347, USA.
Reifsnyder
C
C
McVey
M
M
Gazo
B
B
Pillus
L
L
D000483:Alleles; D001483:Base Sequence; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics*; D020868:Gene Silencing; D051738:Origin Recognition Complex; D010641:Phenotype; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000502:physiology; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D016615:Telomere; D015534:Trans-Activators / Q000235:genetics*
D017931:DNA Primers; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D051738:Origin Recognition Complex; C084121:SIR1 protein, S cerevisiae; C084122:SIR3 protein, S cerevisiae; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators