SUBTLE HYDROPHOBIC INTERACTIONS BETWEEN THE 7TH RESIDUE OF THE ZINC-FINGER LOOP AND THE FIRST BASE OF AN HGATAR SEQUENCE DETERMINE PROMOTER-SPECIFIC RECOGNITION BY THE ASPERGILLUS-NIDULANS GATA FACTOR AREA

A change of a universally conserved leucine to valine in the DNA-bindi ng domain of the GATA factor AreA results in inability to activate som e AreA-dependent promoters, including that of the uapA gene encoding a specific urate-xanthine permease. Some other AreA-dependent promoters become able to function more efficiently than in the wild-type contex t, A methionine in the same position results in a less extreme, but op posite effect, Suppressors of the AreA(Val) mutation mapping in the ua pA promoter show that the nature of the base in the first position of an HGATAR (where H stands for A, T or C) sequence determines the relat ive affinity of the promoter for the wild-type and mutant forms of Are A. In vitro binding studies of wild-type and mutant AreA proteins are completely consistent with the phenotypes in vivo. Molecular models of the wild-type and mutant AreA-DNA complexes derived from the atomic c oordinates of the GATA-1-AGATAA complex account both for the phenotype s observed in vivo and the binding differences observed in vitro. Our work extends the consensus of physiologically relevant binding sites f rom WGATAR to HGATAR, and provides a rationale for the almost universa l evolutionary conservation of leucine at the seventh position of the Zn finger of GATA factors. This work shows inter alia that the sequenc e CGATAGagA-GATAA, comprising two almost adjacent AreA-binding sites, is sufficient to ensure activation of transcription of the uapA gene.