HIGH-ABUNDANCE 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 tenfold greater than two low-abundance receptors, In the absence of high-abundance receptors, cells exhibit a n abnormally low tumble frequency and the ability of the remaining rec eptors to mediate directed migration in spatial gradients is substanti ally compromised. We found that increasing the cellular amount of the low-abundance receptor Trg over a range of dosages did not alleviate t hese defects and thus concluded that high- and low-abundance receptors are distinguished not simply by their different dosages in a wild-typ e cell but also by an inherent difference in activity. By creating hyb rids of the low-abundance receptor Trg and the high-abundance receptor Tsr, we investigated the possibility that this inherent difference co uld be localized to a specific receptor domain and found that the cyto plasmic domain of the high-abundance receptor Tsr conferred the essent ial features of that receptor class on the low-abundance receptor Trg, even though it is in this domain that residue identity between the hc o receptors is substantially conserved.