Member of the two-component regulatory system PmrA/PmrB that plays a role in the regulation of resistance towards polymyxin B and cationic antimicrobial peptides in response to limiting concentrations of Mg(2+) (PubMed:14507375). Functions as a transcriptional activator by direct binding to a cis-acting sequence upstream of the target gene promoters including lipase lipA and pmrH promoters (PubMed:16707691, PubMed:29379484). Autoregulates also its own pmrAB operon under Mg(2+)-limiting conditions (PubMed:14507375, PubMed:16707691). By cationic antimicrobial peptides and by Mg(2+)-limiting conditions. Deletion leads to transcriptional alteration of multiple genes including a large number of genes involved in metal transport, such as the feoAB operon involved in ferrous iron uptake and the mgtE and mgtA operons involved in Mg(2+) transport.