SEQUENCES WITHIN AN UPSTREAM ACTIVATION SITE IN THE YEAST ENOLASE GENE ENO2 MODULATE REPRESSION OF ENO2 EXPRESSION IN STRAINS CARRYING A NULL MUTATION IN THE POSITIVE REGULATORY GENE GCR1

Transcription of the yeast enolase gene ENO2 is reduced 20- to 50-fold in strains carrying a null mutation in the positive regulatory gene GCR1. A small deletion mutation within one of two upstream activation sites (UAS elements) in the 5'-flanking region of ENO2 permitted wild-type levels of ENO2 gene expression in a strain carrying the gcr1 null mutation. These data show that sequences required for UAS element activity in GCR1 strains were required to repress ENO2 expression in a gcr1 strain. Protein factors that specifically bound to this UAS/repression site were identified. We show that the DNA-binding proteins ABFI (autonomously replicating sequence-binding factor) is the major protein which binds the UAS/repression site. Minor DNA-binding activities that interact specifically with the UAS/repression site were also identified an may correspond to proteolytic breakdown products of ABFI. None of the observed binding activities were encoded by the GCR1 structural gene. A double-stranded oligonucleotide that included the UAS/repression site activated trancription of UAS-less ENO1 and ENO2 gene cassettes in vivo to wild-type levels in strains carrying the GCR1 allele as well as the gcr1 null mutation. These latter data show that the UAS/repression site is sufficient for transcriptional activation but is not sufficient to repress transcription of he enolase genes in a gcr1 genetic background.