Neither methylating nor demethylating enzymes are required for bacterial chemotaxis.

Clarification of the information processing system in bacterial sensing has been obtained by studying mutants that lack the capacity to modify receptors covalently. The remaining part of the system is able to receive signals from the receptor, to respond with partial adaptation, and to exhibit a chemotactic response. A cycle of chemical reactions analogous to the rhodopsin-transducin cycle in the visual system is shown to provide the proper characteristics to serve as the bridge between receptor and chemotactic output, which allows adaptation in the absence of covalent protein modifications.