Activates the phosphorylation activity of the protein-arginine kinase McsB (By similarity). May function as an important molecule for oxidative tolerance in various types of stress including that of heavy metals. Binds to Cu(2+), Zn(2+), Co(2+) and Cd(2+) via its CXXC metal binding motifs (PubMed:22126623). Interacts with McsB and CtsR; the CXXC motifs are needed for the binding. Up-regulated by heavy metals such as Cu(2+) and Cd(2+), but Zn(2+) and Co(2+) have no effect. Forms part of an operon with ctsR, mcsB and clpC, which is repressed by CtsR. The mutant where Cys residues of three CXXC motifs are mutated to Ala (Cys-3, Cys-6, Cys-29, Cys-32, Cys-105 and Cys-108) is still able to bind Cu(2+), probably via its fourth CXXC motif, but loses the ability to bind Zn(2+), Co(2+) and Cd(2+). Truncated N-terminus.