A REGULATORY ELEMENT IN THE CHA1 PROMOTER WHICH CONFERS INDUCIBILITY BY SERINE AND THREONINE ON SACCHAROMYCES-CEREVISIAE GENES

CHA1 of Saccharomyces cerevisiae is the gene for the catabolic L-serin e (L-threonine) dehydratase, which is responsible for biodegradation o f serine and threonine. We have previously shown that expression of th e CHA1 gene is transcriptionally induced by serine and threonine. Nort hern (RNA) analysis showed that the additional presence of good nitrog en sources affects induction. This may well be due to inducer exclusio n. To identify interactions of cis-acting elements with trans activato rs of the CHA1 promoter, we performed band shift assays of nuclear pro tein extracts with CHA1 promoter fragments. By this approach, we ident ified a protein-binding site of the CHA1 promoter. The footprint of th is protein contains the ABF1-binding site consensus sequence. This in vitro binding activity is present irrespectively of CHA1 induction. By deletion analysis, two other elements of the CHA1 promoter, UAS1CHA a nd UAS2CHA which are needed for induction of the CHA1 gene were identi fied. Each of the two sequence elements is sufficient to confer serine and threonine induction upon the CYC1 promoter when substituting its upstream activating sequence. Further, in a cha4 mutant strain which i s unable to grow with serine or threonine as the sole nitrogen source, the function of UAS1CHA, as well as that of UAS2CHA, is obstructed.