A protein kinase that phosphorylates Ser and Thr residues. Probably acts to suppress the effects of stress linked to accumulation of reactive oxygen species (By similarity). Probably involved in the extracytoplasmic stress response (PubMed:11594757). Has also a role in LPS synthesis, through regulation of the galETK expression (PubMed:15073317). A protein kinase that phosphorylates Ser and Thr residues. Probably acts to suppress the effects of stress linked to accumulation of reactive oxygen species. Probably involved in the extracytoplasmic stress response. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Monomer. Expression is regulated by the CpxRA two-component regulatory system. Belongs to the SrkA/RdoA protein kinase family.