IME1 encodes a transcriptional activator required for the
transcription of meiosis-specific genes and initiation of meiosis in
Saccharomyces cerevisiae . The transcription of IME1 is
repressed in the presence of glucose, and a low basal level of
IME1 RNA is observed in vegetative cultures with acetate as the
sole carbon source. Upon nitrogen depletion a transient induction in the
transcription of IME1 is observed in MAT a/ MAT alfa
diploids, but not in mat-insufficient strains. An unusual large 5'
region, over 2100 bp long, controls the transcription of IME1 .
This area consists of 11 alternate positive and negative discrete
elements. A 32 bp element designated IREu, activates transcription in
the presence of acetate as the sole carbon source, whereas in the
presence of glucose only a basal level of activity is observed.
Transcriptional activation by this element requires the binding of two
transcriptional activators, Msn2p and its homolog, Msn4p. The RAS/cAPK
pathway transmits a glucose signal that prevents the UAS activity of
IREu. A temperature sensitive mutation in the RAS exchange factor,
CDC25 , promotes high UAS activity in glucose media, while
deletion of the regulatory subunit of cAPK, BCY1 , results in no
UAS activity, even in acetate media. Evidence will be presented on the
mode by which the RAS/cAPK pathway affects the function of Msn2p and
Msn4p, and thus the UAS activity of IREu.
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