The yeast ADR1 protein contains two zinc finger domains that are essential for its role in transcriptional activation of alcohol dehydrogenase (ADH2). These domains are thought to function as DNA-binding structures. An ADR1-,B-galactosidase fusion protein made in Escherichia coli and containing the finger domains of ADR1 binds in vitro in a zinc-dependent manner to DNA fragments containing the two ADH2 upstream activation sequences. The strongest binding is to upstream activation sequence 1, a 22-base-pair palindrome.ADR1 is a nuclear protein which is necessary for transcription of the glucose-repressible alcohol dehydrogenase gene (ADH2) in the yeast Saccharomyces cerevisiae. Repression of ADH2 is apparently maintained by posttranslational regulation of ADR1 (4, 7) rather than by DNA-binding repressors (14). The promoter of ADH2 requires upstream activation sequences (UAS) composed of two elements which function synergistically. UAS1 is a 22-base-pair (bp) inverted repeat which allows ADR1-dependent derepression of ADH2 (27). The UAS2 sequence includes the 25 bp directly upstream of UAS1 and allows ADR1-independent derepression of ADH2 expression (J. Yu, personal communication). ADR1 contains two zinc finger domains (10), similar to those which were first observed in transcription factor IIIA from Xenopus laevis, having the consensus sequence Cys-X24-Cys-X3-Phe-X5-Leu-X2-His-X2-His (5, 19). Zinc finger domains have since been found in several eucaryotic genes thought to be involved in the regulation of transcription (6,18,25,29,30) and in some cases have been shown to bind DNA specifically at regulatory elements (8,15,28). Point mutations in either finger region of ADR1 can give rise to null mutants which are incapable of activating ADH2 expression (3). To understand how ADR1 and other finger proteins bind DNA, we studied the in vitro DNAbinding properties of an ADR1-p-galactosidase fusion protein expressed in Escherichia coli.Binding of ADR1-P-galactosidase to the UAS of ADH2. A polypeptide containing amino acids 17 through 229 of ADR1 fused to P-galactosidase (H. Blumberg, Ph.D. thesis, University of Washington, Seattle, 1987), ADR1-229Z, was expressed in E. coli under the control of the strong, heatinducible A promoter, PR, on plasmid pCQ-A229Z (Fig. 1A) (23). Western blot (immunoblot) analysis of extracts with an anti-3-galactosidase antibody showed that 50% of the fusion protein was proteolyzed to B-galactosidase (data not shown). To investigate ADR1 binding to the ADH2 promoter, gel retardation analysis was performed with crude cell extracts of ADR1-229Z mixed with radiolabeled DNA fragments of the ADH2 promoter (Fig. 1B). Protein-DNA complexes of ADR1-229Z bound to radiolabeled promoter DNA are shown in Fig. 2.