Member of the two-component regulatory system LytR/LytS that regulates genes involved in autolysis, programmed cell death, biofilm formation and cell wall metabolism. Participates also in sensing and responding to host defense cationic antimicrobial peptides (HDPs). Upon phosphorylation by LytS, functions as a transcription regulator by direct binding to promoter regions of target genes including lrgA and lrgB, to positively regulate their expression. Homodimer; when phosphorylated. Phosphorylated and dephosphorylated by LytS.