A protein kinase that (auto)phosphorylates on Ser and Thr residues (PubMed:17302814). Probably acts to suppress the effects of stress linked to accumulation of reactive oxygen species. Protects cells from stress by antagonizing the MazE-MazF TA module, probably indirectly as it has not been seen to phosphorylate MazE, MazF or MazG (PubMed:23416055). Probably involved in the extracytoplasmic stress response (PubMed:9159398). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] May bind 2 Mg(2+) ions. Monomer. Induced by the two-component Cpx system that responds to extracellular stress. A hyperlethal phenotype (reduced survival in the presence of antibiotic but no change in minimal inhibitory concentration) for a number of antimicrobials including nalidixic acid, tetracycline, ampicillin and mitomycin C as well as exposure to UV light and H(2)O(2). Lethality is mitigated by pretreatment with 2,2'-bipyridyl and thiourea, which inhibit hydroxyl radical accumulation. No change in cell survival upon heat shock (up to 55 degrees Celsius), rifampicin or fluoroquinolone PD161144 treatment. A triple srkA-mazE-mazF disruption mutant shows no hyperlethality in the presence of nalidixic acid or UV light, suggesting SrkA has a negative effect on MazF. Double katG-srkA and double cpxR-srkA disruption mutants are as sensitive to killing as single srkA mutants; i.e. all 3 genes are epistatic and function in the same genetic pathway. Belongs to the SrkA/RdoA protein kinase family.