High- and low-abundance chemoreceptors in Escherichia coli: differential activities associated with closely related cytoplasmic domains.

In Escherichia coli, two high-abundance chemoreceptors are present in cellular dosages approximately ten-fold greater than two low-abundance receptors. In the absence of high-abundance receptors, cells exhibit an abnormally low tumble frequency and the ability of the remaining receptors to mediate directed migration in spatial gradients is substantially compromised. We found that increasing the cellular amount of the low-abundance receptor Trg over a range of dosages did not alleviate these defects and thus concluded that high- and low-abundance receptors are distinguished not simply by their different dosages in a wild-type cell but also by an inherent difference in activity. By creating hybrids of the low-abundance receptor Trg and the high-abundance receptor Tsr, we investigated the possibility that this inherent difference could be localized to a specific receptor domain and found that the cytoplasmic domain of the high-abundance receptor Tsr conferred the essential features of that receptor class on the low-abundance receptor Trg, even though it is in this domain that residue identity between the two receptors is substantially conserved.