Member of the two-component regulatory system CrdR/CrdS that induces the transcriptional induction of the copper resistance determinant CrdA (PubMed:12933888). Upon phosphorylation by CrdS, functions as a transcriptional regulator by direct binding to promoter regions of target genes including the crdA promoter or nitric oxide-responsive gene promoters (PubMed:26082024). Phosphorylated by CrdS. Deletion mutant is not able to colonize the stomach in mice (PubMed:12933888). Shows also a significant loss of viability upon exposure to nitric oxide (PubMed:26082024).