The regulator of the @entity375 XXXX utilization pathway is differentially phosphorylated in response to the quality of the @entity1568 source.

@entity73080 @entity73078 @entity1568 @entity7263 @entity73079 @entity3265 @entity1521 @entity375
The @entity1521 utilization pathway in @entity375 is regulated by the @entity73078 transcriptional activator in response to the presence of the inducer @entity1521 and the quality of the @entity1568 source in the growth medium. @entity73078 is constitutively bound to the promoters of its target genes, @entity73079 and @entity73080 , under all conditions studied but activates transcription to the maximum extent only in the absence of rich @entity1568 sources and in the presence of @entity1521 (i.e., when @entity1521 serves as the sole source of @entity1568 ). Changes in target gene expression therefore occur through changes in the activity of the DNA-bound regulator. In this report, we demonstrate by phosphatase treatment of immunoprecipitates of extracts metabolically labeled with @entity7263 or (35)S that @entity73078 is a phosphoprotein. Examination of @entity73078 isolated from cells grown on a variety of @entity1568 sources showed that it was differentially phosphorylated as a function of the quality of the @entity1568 source: the poorer the @entity1568 source, the slower the gel migration of the phosphoforms. The presence of the inducer does not detectably alter the phosphorylation profile. Activator-defective and activator-constitutive @entity73078 mutants have been analyzed. One activator-defective mutant appears to be phosphorylated in a pattern similar to that of the wild type, thus separating its ability to be phosphorylated from its ability to activate transcription. Three activator-constitutive mutant proteins from cells grown on an @entity3265 -containing medium have a phosphorylation profile similar to that of the wild-type protein in cells grown on @entity1521 . These results demonstrate a correlation between the phosphorylation status of @entity73078 and its ability to activate its target genes and suggest that there are two signals, @entity1521 induction and quality of @entity1568 source, impinging on @entity73078 that act synergistically for maximum expression of the @entity1521 utilization pathway.
