The HO gene in Saccharomyces cerevisiae is regulated by a large and complex promoter that is similar to promoters in higher order eukaryotes. Within this promoter are 10 potential binding sites for the a1-alpha2 heterodimer, which represses HO and other haploid-specific genes in diploid yeast cells. We have determined that a1-alpha2 binds to these sites with differing affinity, and that while certain strong-affinity sites are crucial for repression of HO, some of the weak-affinity sites are dispensable. However, these weak-affinity a1-alpha2-binding sites are strongly conserved in related yeast species and have a role in maintaining repression upon the loss of strong-affinity sites. We found that these weak sites are sufficient for a1-alpha2 to partially repress HO and recruit the Tup1-Cyc8 (Tup1-Ssn6) co-repressor complex to the HO promoter. We demonstrate that the Swi5 activator protein is not bound to URS1 in diploid cells, suggesting that recruitment of the Tup1-Cyc8 complex by a1-alpha2 prevents DNA binding by activator proteins resulting in repression of HO.
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| Gene/Complex | Qualifier | Gene Ontology Term | Annotation Extension | Evidence | Source | Assigned On |
|---|---|---|---|---|---|---|
| Mating-type MATalpha2-MATa1 complex | enables | DNA-binding transcription repressor activity, RNA polymerase II-specific | IPI | ComplexPortal | 2018-05-03 | |
| Mating-type MATalpha2-MATa1 complex | involved in | regulation of mating-type specific transcription, DNA-templated | IDA | ComplexPortal | 2023-01-11 | |
| MATALPHA2 | enables | DNA-binding transcription repressor activity, RNA polymerase II-specific | IDA | SGD | 2013-08-07 |