COEXPRESSION OF THE LONG AND SHORT FORMS OF CHEA, THE CHEMOTAXIS HISTIDINE KINASE, BY MEMBERS OF THE FAMILY ENTEROBACTERIACEAE

CheA is the histidine protein kinase of a two-component signal transdu ction system required for bacterial chemotaxis, Motile cells of the en teric species Escherichia coli and Salmonella typhimurium synthesize t wo forms of CheA by utilizing in-frame initiation sites within the gen e cheA. The full-length protein, CheA(L), plays an essential role in t he chemotactic signaling pathway, In contrast, the function of the sho rt form, CheA(S), remains elusive. Although CheA(S) lacks the histidin e residue that becomes phosphorylated in CheA(L), it exhibits both kin ase activity and the ability to interact with and enhance the activity of CheZ, a chemotaxis protein that accelerates dephosphorylation of t he two-component response regulator CheY, To determine whether other m embers of the family Enterobacteriaceae express CheA(S) and CheZ, we a nalyzed immunoblots of proteins from clinical isolates of a variety of enteric species, All motile, chemotactic isolates that we tested coex pressed CheA(L), CheA(S), and CheZ, The only exceptions were closely r elated plant pathogens of the genus Erwinia, which expressed CheA(L) a nd CheZ but not CheA(S). We also analyzed nucleotide sequences of the cheA loci from isolates of Serratia marcescens and Enterobacter cloaca e, demonstrating the presence of in-frame translation initiation sites similar to those observed in the cheA loci of E. coli and S, typhimur ium. Since coexpression of CheA(S) and CheZ appears to be limited to m otile, chemotactic enteric bacteria, we propose that CheA(S) may play an important role in chemotactic responses in some environmental niche s encountered by enteric species.