Identification of a positive regulatory protein in Escherichia coli: the product of the cysB gene.

From the specialized transducing bacteriophage lambdacysB, recombinant phages lambdacysB242 and lambdacysB257 have been obtained, each of which carries an amber mutation in the cysB cistron. A comparison of polyacrylamide gel electrophoretic profiles of labelled extracts from uv-irradiated bacteria that had been infected with lambdacysB+ or with lambdacysB-amber phages, led to the identification of a 39,000-dalton polypeptide as the product of the cysB gene. The native protein was purified to near radiochemical purity and was found to be an oligomer with an isoelectric point close to pH 7.