Transcriptional regulation of meiosis in budding yeast

4. The SIN3, UME6, and RPD3 genes. UME6 encodes a C6Zn2 protein that binds the
URS1 sequence present in many genes including EMG (Anderson et al., 1995; Strich et al.,
1994). The C6Zn2 domain is sufficient for binding, and is required for its repression activity
(Anderson et al., 1995; Strich et al., 1994). Deletion of UME6 causes high expression of EMG, as
well as additional non-meiotic genes carrying the URS1 element, in vegetative growth conditions
(Bowdish and Mitchell, 1993; Lopes et al., 1993; Park et al., 1992; Strich et al., 1994). In
addition, Ume6 functions as a transcriptional repressor when tethered to heterologous genes
following its fusion to lexA (Kadosh and Struhl, 1997). This repression activity of Ume6 depends
on the availability of Sin3 (Ume4, Rpd1) and Rpd3 (Kadosh and Struhl, 1997).
Coimmunoprecipitation and two-hybrid assays demonstrate physical association between
Ume6(515-530) and Sin3(426-472) (the PAH2 domain), as well as between Sin3 and Rpd3
(Kadosh and Struhl, 1997; Kasten et al., 1997; Washburn and Esposito, 2001).
Sin3 functions as a transcriptional repressor when tethered to heterologous genes following its
fusion to lexA (Wang and Stillman, 1993). The repression activity of Sin3 depends on Rpd3
(Kadosh and Struhl, 1997; Kasten et al., 1997). In accord, the double mutant sin3 rpd3 have the
same phenotype as either single mutant (Vidal and Gaber, 1991).
RPD3 encodes histone deacetylase whose deletion, similar to SIN3 deletion, causes an increase
in acetylation of lysines 5 and 12 in histone H4 in various genes carrying the URS1 element
(Burgess et al., 1999; Rundlett et al., 1998). Recruitment of the Sin3/Rpd3 complex by Ume6 to
DNA results in decreased acetylation of histone H3 and H4 in a restricted region, up to two
nucleosomes from the binding site of Ume6 (Kadosh and Struhl, 1998).
5. The ISW2 gene. Isw2 in a complex with Itc1 functions as an ATP dependent chromatinremodeling
factor that is required for the repression of EMG under vegetative growth conditions
(Goldmark et al., 2000). Isw2 functions in parallel to the Sin3/Rpd3 histone deacetylase complex,
as deduced from the observation that the level of expression of EMG are dramatically increased
in the sin3 isw2 double mutant in comparison to the single mutants (Goldmark et al., 2000). Isw2
physically associates with Ume6, and since it’s binding to the URS1 element depends on Ume6,
it was concluded that Ume6 recruits the Isw2 complex to URS1 (Goldmark et al., 2000). DNaseI
and micrococcal nuclease digestion of the chromatin near the EMG REC104 show dependence on
Isw2, suggesting that the Isw2 complex forms an inaccessible chromatin structure near the URS1
element (Goldmark et al., 2000). These results suggest that Isw2 would be localized to the
nucleus in vegetative growth media. However, this is not the case, Isw2 is localized to the
cytoplasm in vegetative growth cultures, and to the nucleus, the cytoplasmic and spindle
microtubuli, in meiotic cultures (Trachtulcova et al., 2000). There is no good explanation to
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