The
DNA-binding protein Ume6 is required for both repression and
activation of many meiosis-specific genes in S. cerevisiae,
through interaction with the corepressor Sin3 and meiotic activator
Ime1, respectively. We find that fusion of a transcriptional
activation domain to Ume6 is unable to convert it into a constitutive
activator, indicating an additional function is needed to overcome
repression. Mutations in UME6 allowing the fusion to activate
cause loss of repression and lie in a predicted amphipathic
alpha-helix. They disrupt interaction with Sin3 in vitro and
in vivo and precisely define the Ume6 Sin3-binding domain,
which interacts with the PAH2 region of Sin3. Our analysis indicates
(1) Ime1 may play a dual role in providing both an activation domain
and relieving Sin3-mediated repression, (2) premature expression and
lack of rerepression of Ume6/Sin3-regulated genes is not deleterious
to subsequent meiotic progression, and (3) since Sin3, but not its
interaction with Ume6, is required for sporulation, Sin3 must play
another, Ume6-independent, role in meiosis. We have also used DNA
oligonucleotide microarrays to define the complete profile of
UME6-regulated genes. 75 genes derepressed in ume6
deletion mutants contain the URS1 Ume6-binding site and are therefore
likely direct targets. They include metabolic and sporulation
functions. Among these, 34 are meiotically regulated in wild-type
cells, mostly, but not exclusively, in the early expression class.
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