The ArsR protein is a trans ‐acting regulatory protein

Summary The arsR gene encodes the regulatory protein of the plasmid‐encoded arsenical resistance operon. A series of in‐frame fusions was constructed between the C ‐terminally truncated arsR gene and the coding region for the mature form of β‐lactamase (blaM). Fusions containing most of the arsR gene were still inducible by arsenicals. Fusions containing less than 102 residues of the 117‐residue ArsR protein were constitutive. When a wild‐type arsR gene was placed in trans , the constitutive constructs were again inducible. The results demonstrate that the ArsR protein is a trans‐acting regulatory protein which controls its own expression.