Member of the two-component regulatory system MprB/MprA which contributes to maintaining a balance among several systems involved in stress resistance and is required for establishment and maintenance of persistent infection in the host. Functions as a transcriptional regulator that recognizes a 19-bp nucleotide motif comprizing two loosely conserved 8-bp direct DNA-binding motif repeats separated by a 3-bp spacer region. MprB/MprA is involved in regulation of numerous stress-responsive genes, including up-regulation of two sigma factors, sigE and sigB as well as pepD and mprA, and repression of multiple genes from regulons associated with hypoxia, starvation and iron metabolism. The majority of genes regulated by MprB/MprA under a particular stress condition are different from those induced during normal growth, but several genes are commonly regulated under more than one condition. Monomer. Interaction with each conserved 8-bp repeat requires tandem binding by two protein monomers (Probable). Autoregulated. Differentially up-regulated under different stress conditions, such as low concentrations of detergents and alkaline pH. Induced by low concentrations of sodium dodecyl sulfate (SDS) in a SigE-dependent manner. In strain ATCC 25618 / H37Rv, repressed during growth in macrophages. Phosphorylated and dephosphorylated by MprB. Phosphorylation is not required for binding to DNA in vitro. However, phosphorylation enhances DNA binding and is required for activity in vivo. Truncated N-terminus.