Cloning and Characterization of Four SIR Genes of Saccharomyces cerevisiae

Abstract

Mating type in the yeast Saccharomyces cerevisiae is determined by the MAT (a or alpha) locus. HML and HMR, which usually contain copies of alpha and a mating type information, respectively, serve as donors in mating type interconversion and are under negative transcriptional control. Four trans-acting SIR (silent information regulator) loci are required for repression of transcription. A defect in any SIR gene results in expression of both HML and HMR. The four SIR genes were isolated from a genomic library by complementation of sir mutations in vivo. DNA blot analysis suggests that the four SIR genes share no sequence homology. RNA blots indicate that SIR2, SIR3, and SIR4 each encode one transcript and that SIR1 encodes two transcripts. Null mutations, made by replacement of the normal genomic allele with deletion-insertion mutations created in the cloned SIR genes, have a Sir- phenotype and are viable. Using the cloned genes, we showed that SIR3 at a high copy number is able to suppress mutations of SIR4. RNA blot analysis suggests that this suppression is not due to transcriptional regulation of SIR3 by SIR4; nor does any SIR4 gene transcriptionally regulate another SIR gene. Interestingly, a truncated SIR4 gene disrupts regulation of the silent mating type loci. We propose that interaction of at least the SIR3 and SIR4 gene products is involved in regulation of the silent mating type genes.

Adaptive Potential of Epigenetic Switching During Adaptation to Fluctuating Environments

“…However, in the presence of a drug, 5-fluoroorotic acid (5-FOA), the activity of the Ura3 protein is deleterious, because it converts the drug into a toxic 5-fluorouracil that kills the cell ( Boeke et al 1987 ). The strength of the silencing and the rate of switching between ON and OFF state of URA3 expression in the subtelomeric region are dependent on the activity of silent information regulator (SIR) proteins ( Ivy et al 1986 ; Rine and Herskowitz 1987 ; Aparicio et al 1991 ), which act as chromatin modifiers ( Imai et al 2000 ), and the relative distance of the gene from the telomere ( Pryde and Louis 1999 ). Using this well-established system, we selected URA3 gene activation (ON state) by removing uracil from the medium, or inactivation (OFF state) by adding 5-FOA.…”

miRNA in Parkinson's disease: From pathogenesis to theranostic approaches

“…Sirtuins (SIRT) are proteins that seem to be class 3 histone deacetylases (HDACs) that are reliant on nicotinamide adenine dinucleotide (NAD+), which has a significant impact on neurodegenerative illnesses (Shoba et al, 2009). The family consists of seven members in mammals from SIRT1-SIRT7 (Ivy et al, 1986). It possesses two different activities: an ADP ribosyl transferase activity and/or a deacetylase activity (Landry et al, 2000;Liszt et al, 2005) Sirtuins induces neurodegenerative diseases either by mitochondrial function and energy metabolism regulation.…”

Novel Role of the SIRT1 in Endocrine and Metabolic Diseases

“…Sirtuins is also known as silent information regulator 2 (Sir2) 21 , 22 . Increasing the dosage or activity of Sir2 has been shown to extend the life spans of yeast, worms, and flies, while deletions or mutations of the Sir2 reverses the result 21 , 23 , 24 .…”