Rim101 and Nrg1 bind to a bipartite regulatory element to direct repression of DIT1 and DIT2 during vegetative growth in Saccharomyces cerevisiae.
Karen Rothfels (1), Jason Tanny (2), Eniko Molnar (2), Cosimo Commisso (3), Helena Friesen (3), Jacqueline Segall (3)
(1) Department of Biochemistry, University of Toronto, Toronto, ON;
(2) Department of Molecular and Medical Genetics, University of Toronto, Toronto, ON;
(3) Department of Biochemistry, University of Toronto, 1 King's College, Toronto, ON, M5S 1A8, Canada
DIT1 and DIT2 are divergently transcribed sporulation-specific genes of S. cerevisiae required for spore wall maturation. Repression of these genes in mitotically growing cells is mediated by Ssn6-Tup1 and depends on a 42 bp negative regulatory element (NRE) present in the DIT1-DIT2 intergenic region. The NRE contains two distinct subsites. Each of these, when multimerized, supports efficient Ssn6-Tup1 dependent repression of a CYC1-(NRE)-lacZ reporter gene in mitotic cells. In a classic genetic screen we identified RIM101 as a potential NRE-binding protein. Rim101 has similarity to the A. nidulans protein PacC, a pH-responsive DNA-binding transcription factor with a defined target site that is also present in the downstream portion of NRE42. We have shown that Rim101 binds this site both in vitroand in vivo. A screen of the collection of yeast deletion strains identified NRG1 as a potential regulator that acts through the upstream portion of NRE42. We have shown that Nrg1 binds to this upstream region in vitro. Nrg1 is a known DNA-binding, Ssn6-Tup1 dependent transcriptional repressor. It is intriguing to note that both Nrg1 and Rim101 are zinc-finger (Cys2-His2) containing proteins that are involved in invasive growth and pH response. We are currently investigating the mechanism by which Nrg1 and Rim101 cooperate to mediate high levels of repression through the bipartite NRE.
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