DNA-BINDING CHARACTERISTICS OF REGA - A CONSTITUTIVELY ACTIVE ANAEROBIC ACTIVATOR OF PHOTOSYNTHESIS GENE-EXPRESSION IN RHODOBACTER-CAPSULATUS

In the purple non-sulfur bacterium Rhodobacter capsulatus, RegA and Re gB comprise a two-component regulatory system that is required for max imal anaerobic transcription of key photosynthesis genes. RegB is a se nsor kinase that uses ATP to phosphorylate its cognate response regula tor, RegA, The mechanism under which RegA similar to P influences tran scription of target genes has been unclear given that past attempts to demonstrate DNA binding activity by isolated RegA have failed. This l ed to a model invoking a role for RegA similar to P as an intermediate in a more complex multicomponent phosphoryl transfer cascade. In the present study, we describe the isolation of a mutant version of RegA ( RegA) which promotes high level expression of photosynthesis genes in dependent of RegB. DNase I footprint analyses show that purified RegA binds to the promoters of the puf and puc operons at locations that a re consistent with RegA functioning as a transcriptional activator for these operons. We conclude that RegA functions, like most members of the response regulator family, as a DNA-binding protein that directly affects the expression of its target genes.