A BIPARTITE OPERATOR INTERACTS WITH A HEAT-SHOCK ELEMENT TO MEDIATE EARLY MEIOTIC INDUCTION OF SACCHAROMYCES-CEREVISIAE HSP82

Although key genetic regulators of early meiotic transcription in Sacc haromyces cerevisae have been well characterized, the activation of me iotic genes is still poorly understood in terms of cis-acting DNA elem ents and their associated factors, I report here that induction of HSP 82 is regulated by the early meiotic IME1-IME2 transcriptional Cascade , Vegetative repression and meiotic induction depend on interactions o f the promoter-proximal heat shock element (HSE) with a nearby biparti te repression element, composed of the ubiquitous early meiotic motif, URS1 (upstream repression sequence 1), and a novel ancillary repressi on element. The ancillary repression element is required for efficient vegetative repression, is spatially separable from URS1, and continue s to facilitate repression during sporulation, In contrast, URS1 also functions as a vegetative repression element but is converted early in meiosis into an HSE-dependent activation element. An early step in th is transformation may be the antagonism of URS1-mediated repression by IME1. The HSE also nonspecifically supports a second major mode of me iotic activation that does not require URS1 but does require expressio n of IME2 and concurrent starvation. Interestingly, increased rather t han decreased URS1-mediated vegetative transcription can be artificial ly achieved by introducing rare point mutations into URS1 or by deleti ng the UME6 gene. These lesions offer insight into mechanisms of URS-d ependent repression and activation, Experiments suggest that URS1-boun d factors functionally modulate heat shock factor during vegetative tr anscription and early meiotic induction but not during heat shock. The loss of repression and activation observed when the IME2 activation e lement, T4C, is substituted for the HSE suggests specific requirements for URS1-upstream activation sequence interactions.