A eukaryotic transcriptional activator bearing the DNA specificity of a prokaryotic repressor.

We describe a new protein that binds to DNA and activates gene transcription in yeast. This protein, LexA-GAL4, is a hybrid of LexA, an Escherichia coli repressor protein, and GAL4, a Saccharomyces cerevisiae transcriptional activator. The hybrid protein, synthesized in yeast, activates transcription of a gene if and only if a lexA operator is present near the transcription start site. Thus, the DNA binding function of GAL4 can be replaced with that of a prokaryotic repressor without loss of the transcriptional activation function. These results suggest that DNA-bound LexA-GAL4 and DNA-bound GAL4 activate transcription by contacting other proteins.