Member of the two-component regulatory system PrrB/PrrA that is involved specifically in early intracellular multiplication of Mycobacterium and is essential for its viability. Upon phosphorylation by PrrB, functions as a transcription regulator by direct binding to promoter regions of target genes to positively regulate their expression. Autoregulates its own expression. Phosphorylated by PrrB at Asp-58. Extended N-terminus.