Affiliation:
1. Department of Molecular and Medical Genetics
2. Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8
Abstract
ABSTRACT
The
NDT80
gene of
Saccharomyces cerevisiae
, which encodes a global activator of transcription of middle sporulation-specific genes, is first expressed after the activation of early meiotic genes but prior to activation of middle sporulation-specific genes. Both upstream repression sequence 1 (URS1) and mid-sporulation element (MSE) sites are present in the promoter region of the
NDT80
gene; these elements have been shown previously to contribute to the regulation of expression of early and middle sporulation-specific genes, respectively, by mediating repression in growing cells and activation at specific times during sporulation. In this study, we have shown that the overlapping windows of URS1- and MSE-mediated repression and activation are responsible for the distinctive premiddle expression pattern of the
NDT80
gene. Our data suggest that a Sum1-associated repression complex bound at the
NDT80
MSE sites prevents Ime1 tethered at the
NDT80
URS1 sites from activating transcription of the
NDT80
gene at the time that Ime1-dependent activation of early URS1-regulated meiotic genes is occurring. We propose that a decrease in the efficiency of Sum1-mediated repression as cells progress through the early events of the sporulation program allows the previously inactive Ime1 tethered at the URS1
NDT80
sites to promote a low level of expression of the
NDT80
gene. This initial phase of URS1-dependent
NDT80
expression is followed by Ndt80-dependent upregulation of its own expression, which requires the MSE
NDT80
sites and occurs concomitantly with Ndt80-dependent activation of a set of middle MSE-regulated sporulation-specific genes. Mutation of
IME2
prevents expression of
NDT80
in sporulating cells. We show in this study that
NDT80
is expressed and that middle genes are activated in cells of an Δ
ime2/
Δ
ime2
Δ
sum1/
Δ
sum1
strain in sporulation medium. This suggests that Ime2 activates expression of
NDT80
by eliminating Sum1-mediated repression.
Publisher
American Society for Microbiology
Subject
Cell Biology,Molecular Biology
Cited by
81 articles.
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