MECHANISMS OF METALLOREGULATION OF AN ANION-TRANSLOCATING ATPASE

The ars (arsenical resistance) operon cloned from R-factor R773 has fi ve genes that encode two repressor proteins, ArsR and ArsD, and three structural proteins, ArsA, ArsB, and ArsC. The ArsA and ArsB proteins form a membrane-bound pump that functions as an oxyanion-translocating ATPase. The substrates of the pump are the oxyanions arsenite or anti monite. The ArsC protein is an arsenate reductase that reduces arsenat e to arsenite, which is subsequently pumped out of the cell. This revi ew deals with the mechanism of transcriptional regulation by the ArsR repressor and allosteric regulation of the ArsA protein, the catalytic subunit of the pump. The chemical nature of the inducer plays an impo rtant role in regulation. In solution arsenite or antimonite exist as oxyanions and reacts with the cysteines in proteins. In both transcrip tional regulation by the ArsR repressor and allosteric regulation of t he ArsA ATPase, the ability of As(III) and Sb(III) to interact with th e cysteines of the proteins, involves their action as effector.