ADR1 super(c) mutations enhance the ability of ADR1 to activate transcription by a mechanism that is independent of effects on cyclic AMP-dependent protein kinase phosphorylation of Ser-230

We have isolated and characterized an additional 17 ADR1 super(c) mutations, defining 10 different amino acid changes, that were located in the region defined by amino acids 227 through 239 of ADR1. Three observations, however, indicate that the ADR1 super(c) phenotype is not simply equivalent to a lack of cAPK phosphorylation. First, only some of these newly isolated ADR1 super(c) mutations affected the ability of yeast cAPK to phosphorylate corresponding synthetic peptides modeled on the 222 to 234 region of ADR1 in vitro. Second, we observed that strains lacking cAPK activity did not display enhanced ADH2 expression under glucose growth conditions. Third, when Ser-230 was mutated to a nonphosphorylatable residue, lack of cAPK activity led to a substantial increase in ADH2 expression under glucose-repressed conditions. Thus, while cAPK controls ADH2 expression and ADR1 is required for this control, cAPK acts by a mechanism that is independent of effects on ADR1 Ser-230.