Toxic component of a type II toxin-antitoxin (TA) system; overexpression in wild-type temporarily inhibits cell growth, overexpression in a hipAB deletion leads to acute growth inhibition. The toxic effect of HipA is neutralized by its cognate antitoxin HipB. In the ternary phosphoserine-HipA-HipB-DNA complex the DNA is bent about 125 degrees; all HipA in the crystallized ternary complex is phosphorylated. In E.coli phosphorylation of HipA is thought to release HipB from the HipA-HipB-DNA complex, suggesting the complex functions differently in the 2 bacteria (PubMed:25056321). Phosphorylates Glu-tRNA-ligase (GltX, on 'Ser-239') in vivo, with HipB probably acts as a corepressor for transcription of the hipBA promoter (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. Forms a HipA(2)HipB(2)-DNA complex with cognate antitoxin HipB; has higher affinity for the latter when HipB is prebound to DNA and HipA is phosphorylated. Binds DNA in the ternary complex. Expressed in late-exponential phase; part of the hipBA operon. 50% decrease in biofilm. Belongs to the HipA Ser/Thr kinase family.