A protein kinase that (auto)phosphorylates on Ser and Thr residues, probably involved in the extracytoplasmic stress response (PubMed:12511488). Probably acts to suppress the effects of stress linked to accumulation of reactive oxygen species (By similarity). 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 growth phase dependent and sensitive to the media conditions reaching high levels in stationary phase (at protein level) (PubMed:17302814). It is probably regulated by the CpxRA two-component regulatory system (PubMed:12511488). Decreases long-term survival (1000-fold decrease after 20 days in liquid culture), derepresses curli production under non-curli-inducing growth conditions. Belongs to the SrkA/RdoA protein kinase family.