ADR1-mediated regulation of ADH2 requires an inverted repeat sequence

DNA sequence analysis of wild-type and mutant ADH2 loci suggested that two unusual features 5' of the promoter, a 22-base-pair perfect dyad sequence and a (dA)20 tract, were important for regulation of this gene (D. W. Russell, M. Smith, D. Cox, V. M. Williamson, and E. T. Young, Nature [London] 304:652-654, 1983). Oligonucleotide-directed mutagenesis was used to construct ADH2 genes lacking the 22-base-pair dyad or the (dA)20 tract (V.-L. Chan and M. Smith, Nucleic Acids Res. 12:2407-2419, 1984). These mutant genes and other ADH2 deletions constructed by BAL 31 endonuclease digestion were studied after replacing the wild-type chromosomal locus with the altered alleles by the technique of gene transplacement (T. L. Orr-Weaver, J. W. Szostak, and R. S. Rothstein, Proc. Natl. Acad. Sci. USA 78:6354-6358, 1981), using canavanine resistance as the selectable marker. Deletions lacking the dyad failed to derepress normally and did not respond to mutations at the ADR1 locus, which encodes a protein necessary to activate ADH2. Deletions of the (dA)20 tract did not have a detectable phenotype. A small deletion located just 3' to the (dA)20 tract (between positions -164 and -146) had a low amount of ADR1-dependent transcription during repressed growth conditions, indicating that the regulatory protein encoded by ADR1 is present in a potentially active form during repression and that alterations of a DNA sequence in the promoter region can unmask its latent activity.