Attractants and repellents control demethylation of methylated chemotaxis proteins in Escherichia coli.

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Abstract
A group of methylated proteins, the methyl-accepting chemotaxis proteins (MCP), has been shown to play a central role in bacterial chemotaxis. Both methylation and demethylation of MCP occur continuously in the absence of added stimuli; these two processes are in balance such that a basal level of methylation is maintained. Attractants cause the methylation level to increase to a new value, whereas repellents bring about a decrease in level. Therefore, attractants and repellents must somehow perturb the balance between methylation and demethylation of MCP. In this report the effect of attractants on demethylation of MCP was monitored in two ways: (i) by following the disappearance of [methyl-3H]MCP and (ii) by measuring formation of [3H]methanol, the product of MCP demethylation. Both methods showed that addition of attractants causes a transient inhibition of MCP demethylation. Repellent addition has previously been shown to stimulate MCP demethylation. It is therefore concluded that control of demethylation plays a crucial role in changing the level of methylation of MCP in response to attractants and repellents.