Jm. Skidmore et al., Polar clustering of the chemoreceptor complex in Escherichia coli occurs in the absence of complete CheA function, J BACT, 182(4), 2000, pp. 967-973
Bacterial chemotaxis requires a phosphorelay system initiated by the intera
ction of a ligand with its chemoreceptor and culminating in a change in the
directional bias of flagellar rotation. Chemoreceptor-CheA-CheW ternary co
mplexes mediate transduction of the chemotactic signal. In vivo, these comp
lexes cluster predominantly in large groups at the cell poles. The function
of chemoreceptor clustering is currently unknown. To gain insight into the
relationship between signaling and chemoreceptor clustering, we examined t
hese properties in several Escherichia coil mutant strains that produce Che
A variants altered in their ability to mediate chemotaxis, autophosphorylat
e, or bind ATP. We show here that polar clustering of chemoreceptor complex
es does not require functional CheA protein, although maximal clustering oc
curred only in chemotactically competent cells. Surprisingly, in cells cont
aining a minimum of 13 gold particles at the cell pole, a significant level
of clustering was observed in the absence of CheA, demonstrating that CheA
is not absolutely essential for chemoreceptor clustering. Nonchemotactic c
ells expressing only CheA(S), a C-terminal CheA deletion, or CheA bearing a
mutation in the ATP-binding site mediated slightly less than maximal chemo
receptor clustering. Cells expressing only full-length CheA (CheA(L)) from
either a chromosomal or a plasmid-encoded allele displayed a methyl-accepti
ng chemotaxis protein localization pattern indistinguishable from that of s
trains carrying both CheA(L) and CheA(S), demonstrating that CheA(L) alone
can mediate polar clustering.