MUTATIONS IN A DISPENSABLE REGION OF THE UAY TRANSCRIPTION FACTOR OF ASPERGILLUS-NIDULANS DIFFERENTIALLY AFFECT THE EXPRESSION OF STRUCTURAL GENES

The uaY gene encodes a transcriptional activator mediating uric acid i nduction of at least nine genes of the purine-utilization pathway, In this article, we characterize a loss-of-function mutation, uaY205, as a 16 bp deletion that results in premature translation termination, an d substitutes the C-terminal 63 amino acids for 13 amino acid residues . Reversion analysis demonstrates that the C-terminal 63 amino acid re sidues are unnecessary for UaY function, and that the loss-of-function phenotype resulting from the uaY205 mutation is caused by the new ami no acid sequence present in the mutant protein. Revertants in two diff erent frames (wild type and +1) restore function but show subtle diffe rences in the expression of genes controlled by the UaY protein. Two s trains showing elevated expression of genes under UaY control were sho wn to carry, in addition to a mutation leading to the recovery of the wild-type open reading frame, mutations in unlinked genes, Using crude extracts of Aspergillus nidulans, we have been able to detect, for th e first time, in transcription factors of this class, specific retarda tion of a promoter probe, The binding activity is at least partially d ependent on the presence of inducer. The gel shift experiments show th at the novel inhibitory sequence present in the UaY205 protein can act either by affecting the stability of the protein, or via an inter- or intramolecular interaction impairing the specific DNA-binding activit y.