MULTIPLE AND DISTINCT ACTIVATION AND REPRESSION SEQUENCES MEDIATE THEREGULATED TRANSCRIPTION OF IME1, A TRANSCRIPTIONAL ACTIVATOR OF MEIOSIS-SPECIFIC GENES IN SACCHAROMYCES-CEREVISIAE

IME1 encodes a transcriptional activator required for the transcriptio n 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 depleti on a transient induction in the transcription of IME1 is observed in M ATa/MAT alpha diploids but not in MAT-insufficient strains, In this st udy we demonstrate that the transcription of IME1 is controlled by an extremely unusual large 5' region, over 2,100 bp long. This area is di vided into four different upstream controlling sequences (UCS), UCS2 p romotes the transcription of IME1 in the presence of a nonfermentable carbon source, UCS2 is flanked by three negative regions: UCS1, which exhibits URS activity in the presence of nitrogen, and UCS3 and UCS4, which repress the activity of UCS2 in MAT-insufficient cells, UCS2 con sists of alternate positive and negative elements: three distinct cons titutive URS elements that prevent the function of any upstream activa ting sequence (UAS) under all growth conditions, a constitutive UAS el ement that promotes expression under all growth conditions, a UAS elem ent that is active only in vegetative media, and two discrete elements that function as UASs in the presence of acetate, Sequence analysis o f IME1 revealed the presence of two almost identical 30- to 32-bp repe ats, Surprisingly, one repeat, IREd, exhibits constitutive URS activit y, whereas the other repeat, IREu, serves as a carbon-source-regulated UAS element, The RAS-cyclic AMP-dependent protein kinase cAPK pathway prevents the UAS activity of IREu in the presence of glucose as the s ole carbon source, while the transcriptional activators Msn2p and Msn4 p promote the UAS activity of this repeat in the presence of acetate, We suggest that the use of multiple negative and positive elements is essential to restrict transcription to the appropriate conditions and that the combinatorial effect of the entire region leads to the regula ted transcription of IME1.