SHARED CONTROL OF MALTOSE INDUCTION AND CATABOLITE REPRESSION OF THE MAL STRUCTURAL GENES IN SACCHAROMYCES

Maltose utilization in yeast requires the presence of any one of the f ive unlinked, homologous MAL loci. Transcription of the two structural genes MALT (permease) and MALS (maltase) is induced by maltose and ca tabolite-repressed by glucose. MAL6T and MAL6S share a common 5' inter genic sequence; deletion studies within this sequence revealed a bi-di rectionally functioning upstream activation sequence (UAS(M)) consisti ng of four 11 bp homologous sites. Activation of these sites by the MA LR protein results in the coordinate expression of MAL6T and MAL6S. Th e basal promoter activates MALS expression to a greater extent than MA LT and is located in a region that overlaps UAS(M). Deletion of severa l subsites within the UAS(M) has an asymmetric effect on MAL gene expr ession, having a greater affect on MALT than on MALS. Catabolite repre ssion of MAL6T and MAL6S by glucose is controlled at several levels. U sing disruption mutants, the positively acting MAL1R protein was also found to play a role in catabolite repression of MAL6T and MAL6S.