Transcriptional regulation of meiosis in budding yeast

Fig. 9. A schematic structure of IME1 5’ untranslated region showing the positive and
negative transcription factors which regulate its expression.
The regulated transcription of IME1 is mediated by the combinatorial effect of distinct elements.
The MAT signal is transmitted to UCS4 by Rme1. The activity of Rme1 as a repressor requires
Rgr1 and Sin4. The cAMP/PKA signal transduction pathway transmits the glucose signal to IREu
through two transcription factors, Sok2 and Msn2. In glucose growth media phosphorylation of
Sok2 by PKA promotes its repression activity, whereas phosphorylation of Msn2 sequesters the
protein in the cytoplasm. In acetate growth media Sok2 repression is relieved by a decrease in the
activity of PKA, as well as by the function of Ime1. The increased binding of Msn2 to IREu leads
to transcriptional activation. Yhp1 binds to UASv, however, its activity is not required for the
transcription of IME1. Nitrogen, via Cdc25, regulates the URS activity of UCS1. It is not known
whether the effect of Cdc25 is mediated through the cAMP/PKA and/or MAPK pathways.
Filled box - elements required for transcriptional activation. Open box – elements that whose
function is only to repress transcription. A positive role is marked with an arrow, a negative role
in line. Dashed lines and a question mark – preliminary data.
Fig. 10. The expression and activity of Ime1 are regulated by nutrients.
Schematic representation on how glucose and nitrogen regulates the availability and activity of
Ime1. The nucleus is depicted between the two circular lines, and cell membrane by a heavy line.
A positive role is marked with an arrow, a negative role by a straight line. The transcription of
IME1 is inhibited in the presence of glucose and nitrogen. Translation of IME1 mRNA is
inhibited in the presence of a nitrogen source. In the presence of nitrogen, Ime1is sequestered
from the nuclei due to phosphorylation by Cdc28/Cln. Interaction of Ime1 with Ume6, and
consequently transcriptional activation of early meiosis-specific genes (EMG) is inhibited by
glucose and nitrogen.
Fig. 11. Conditions leading to the choice between silencing and expression of early meiosisspecific
genes.
A. Vegetative growth conditions B. Meiotic conditions.
Ume6 binds to the URS1 element in early-meiosis specific genes (EMG) under all growth
conditions. In vegetative growth conditions Ume6 recruits to repression complexes, Sin3/Rpd3
and Isw2, leading to histone H4 deacetylase and chromatin remodeling, respectively, and
silencing. Under these conditions Rim15 and most probably Rim11 are non-active. The activity
of Rim15 is repressed by PKA (Tpk1,2,3) phosphorylation. Under meiotic conditions (acetate
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