Transcriptional
repression in Saccharomyces cerevisiae
Several epigenetic
silencing phenomena are found in S. cerevisiae, where they
are easily accessible to genetic and biochemical analysis. Three types
of silencing are known (Fig. 1): Repression of the cryptic silent
mating-type loci HML and HMR, telomeric silencing and
repression in the ribosomal DNA (rDNA) locus. One
interest in the lab is to extend this palette and to conduct a survey
of silenced regions in the yeast genome, thus contributing to our
understanding of global genomic organization.
Silencing requires several regulatory proteins, some of which are
shared among the three known silenced loci in yeast (Fig. 2).
For instance, the Silent Information Regulator (SIR) proteins
are likely structural components of silenced chromatin. Additionally,
HM silencing requires flanking cis regulatory sequences,
called silencers, which contain binding sites for proteins and protein
complexes. One of these is the yeast replication initiator
complex ORC, which reveals an interesting connection between
replication initiation and transcriptional silencing.
 Histone acetylation, HATs and HDACs
Research
summary Ann Ehrenhofer-Murray |
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Fig. 1: Silenced regions in the
yeast nucleus
Fig. 2: Organization of the yeast mating-type genes
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