Summary Sensory adaptation of low‐abundance chemoreceptors in Escherichia coli requires assistance from high‐abundance receptors, because only high‐abundance receptors carry the carboxyl‐terminal pentapeptide sequence NWETF that enhances adaptational covalent modification. Using membrane vesicles containing both high‐abundance receptor Tar and low‐abundance receptor Trg, we observed effective assistance in vitro for all three adaptational modifications: methylation, demethylation and deamidation. These results demonstrated that adaptational assistance involves not only the previously documented assistance for methylation but also assistance for the two CheB‐catalysed reactions. We determined rates of assisted methylation and demethylation at many ratios of assisting to assisted receptor. Analysis by a model of assistance indicated one Tar dimer could assist seven Trg dimers in methylation or five in demethylation, defining assistance neighbourhoods. These neighbourhoods were larger than a trimer of homodimers, required only receptors and were minimally affected by
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