Transcriptional repressor for the ars operon. ArsR is a trans-acting regulatory protein which controls its own expression. The repressive effect of ArsR is alleviated by oxyions of +III oxidation state of arsenic, antimony, and bismuth, as well as arsenate (As(V)). ARSR2_ECOLX MPEIASLQLFKILSDETRLGIVLLLREMGELCVCDLCTALEQSQPKTSRHLAMLRESGLLLDRKQGKWVHYRLSPHIPSWAALVIEQAWLSQQDDVQAIARKLASANCSGSGKAVCI arsR Arsenical resistance operon repressor 117