Isolation and characterization of lac fusions to two nitrogen-regulated promoters

Mud1 (Ap, lac, cts)-mediated fusions to argTr and dhuA, two transport operon promoters in Salmonella typhimurium, were isolated and characterized in order to investigate the regulation of these promoters. Using these fusions we showed that these promoters are under nitrogen regulation and that this effect, as well as the response to a promoter-up mutation in dhuA, is at the transcriptional level. We utilized the fusions to determine that the histidine transport operon does not contain any internal promoters. The fusions were also used to screen the promoters for additional modes of regulation: argTr was found to respond to carbon regulation in addition to nitrogen regulation, while dhuA does not. The argTr promoter contains a sequence with good homology to the consensus sequence determined for the cAMP receptor protein binding site. Neither promoter responds to sulfur or phosphate regulation.