TRANSCRIPTIONAL CONTROL MEDIATED BY THE ARCA 2-COMPONENT RESPONSE REGULATOR PROTEIN OF ESCHERICHIA-COLI - CHARACTERIZATION OF DNA-BINDING AT TARGET PROMOTERS

ArcA protein bearing an amino-terminal, oligohistidine extension has b een purified, and its DNA binding activity has been characterized with or without prior incubation with carbamoyl phosphate. Electrophoretic mobility shift assays and DNase I protection assays indicate that whe re the phosphorylated form of the ArcA protein (ArcA-P) is expected to act as a transcriptional repressor (e.g., of lctPRD and gltA-sdhCDAB) , the effect is likely to be mediated by sequestration of cis-controll ing transcriptional regulatory elements. In contrast, in the case of c ydAB, for which ArcA-P is expected to function as a transcriptional ac tivator, two discrete binding sites have been identified upstream of a known promoter, and activation from these sites is likely to be media ted by a mechanism typical of the type I class of prokaryotic transcri ptional activators. An additional ArcA-P binding site has also been lo cated downstream of the known promoter, and a distinct role for this s ite in the regulation of the cydAB operon during anoxic growth transit ions is suggested, These results are discussed within the framework of an overall model of signaling by the Are two-component signal transdu ction system in response to changes in aerobiosis.