Specific DNA binding of GAL4, a positive regulatory protein of yeast.

We show by the following series of experiments that the yeast positive regulatory protein GAL4 binds to four sites in the upstream activating sequence UASG to activate transcription of the adjacent GAL1 and GAL10 genes. GAL4 protein expressed in E. coli protected guanine residues in UASG from methylation by dimethyl sulfate. The same set of protections was seen in vivo in yeast and depended on the GAL4+ allele. This protection pattern is consistent with the idea that GAL4 protein binds to four related 17 bp sequences, each of which displays approximate 2-fold rotational symmetry. A single near-consensus synthetic 17 bp oligonucleotide, installed in front of the yeast GAL1 or CYC1 transcription units, conferred a high level of galactose inducibility upon these genes. Further experiments suggest that one mechanism of glucose repression is inhibition of the binding of GAL4 protein to DNA.