Member of the two-component regulatory system BaeS/BaeR which responds to envelope stress (PubMed:12354228). Activates expression of periplasmic chaperone spy in response to spheroplast formation, indole and P pili protein PapG overexpression (PubMed:12354228). Activates the mdtABCD (PubMed:12107133, PubMed:12107134) and probably the CRISPR-Cas casABCDE-ygbT-ygbF operon (PubMed:21255106). Phosphorylated by BaeS. Increased sensitivity to membrane stress caused by indole or by overexpression of P pili protein PapG; double baeR-cpxR mutants are more sensitive yet (PubMed:12354228). Loss of induction of the CRISPR-Cas casABCDE-ygbT-ygbF operon (PubMed:21255106).