DISSECTION OF THE ADR1 PROTEIN REVEALS MULTIPLE, FUNCTIONALLY REDUNDANT ACTIVATION DOMAINS INTERSPERSED WITH INHIBITORY REGIONS - EVIDENCE FOR A REPRESSOR BINDING TO THE ADR1(C) REGION

The yeast transcriptional activator ADR1 is required for expression of the glucose-repressible alcohol dehydrogenase gene (ADH2), as well as genes involved in glycerol metabolism. The N-terminal half of the ADR 1 protein was shown to contain three separate transactivation domains, including one (TADI) that encompasses the zinc finger DNA-binding dom ain. While TADII and TADIII were shown to be functionally redundant in activating ADH2 expression, deletion of only TADIII impaired ADR1 con trol of glycerol metabolism genes. None of these activation domains ap peared to be carbon source regulated when separated from the ADH2 prom oter context. Interspersed among these activation domains were two reg ions which, when removed, increased ADR1 activity; one was localized t o the site of ADR1c mutations (residues 227 to 239) that allow glucose -insensitive ADH2 expression. The 227-to-239 region blocked ADR1 activ ity independently of the TAD present on ADR1, ADR1 DNA binding, and sp ecific ADH2 promoter sequences. In addition, this region inhibited the function of a heterologous transcriptional activator. These results a re consistent with the existence of an extragenic factor that binds th e ADR1c region and represses ADR1 activity and suggest that other fact ors are responsible for aiding ADR1 in the carbon source regulation of ADH2.