Identification of a regulatory region that mediates glucose-dependent induction of the Saccharomyces cerevisiae enolase gene ENO2.

There are two yeast enolase genes, designated ENO1 and ENO2, which are expressed differentially in vegetative cells grown on glucose and in cells grown on gluconeogenic carbon sources. ENO2 is induced more than 20-fold in cells grown on glucose, whereas ENO1 expression is similar in cells grown on glucose and in cells grown on gluconeogenic carbon sources. Sequences within the 5' flanking region of ENO2 which are required for glucose-dependent induction were identified by deletion mapping analysis. These studies were carried out by using a fused gene containing the ENO2 5' flanking sequences and the ENO1 coding sequences. This fused gene undergoes glucose-dependent induction and is expressed at the same level as the resident ENO2 gene in cells grown on glucose or gluconeogenic carbon sources. Expression of fused genes containing deletion mutations within the ENO2 5' flanking region was monitored after integration at the ENO1 locus of a strain carrying a deletion of the resident ENO1 coding sequences. This analysis showed that there are two upstream activation sites located immediately upstream and downstream from a position 461 base pairs upstream from the transcriptional initiation site. Either one of these upstream activation sites is sufficient for glucose-dependent induction and normal gene expression in the presence of gluconeogenic carbon sources. Deletion of both regulatory regions results in a complete loss of gene expression. The regulatory regions function normally in both orientations relative to the coding sequences. Mutant fused genes containing small deletions within the regulatory regions were constructed; these genes were expressed normally in gluconeogenic carbon sources but were not induced in the presence of glucose. Based on this analysis, ENO2 contains a cis-acting regulatory region which is required for gene expression and mediates glucose-dependent induction of gene expression.