Contributions made by individual methylation sites of the Escherichia coli aspartate receptor to chemotactic behavior.

To determine the extent to which chemotactic behavior depends on methylation at multiple sites, chemotaxis assays were performed on bacteria that expressed mutant aspartate receptors in which methylation site residues were mutated from glutamate to aspartate. It was found that chemotaxis was impaired when methylation sites were mutated and that the effect on chemotaxis of mutating a rapidly methylated site was more severe than the effect of mutating a less-rapidly methylated site. Expression of mutant receptors in a wild-type strain interfered with chemotaxis to only a minor extent. In vivo methylation assays showed that the chemotactic defects of most mutants could be explained by the decreased rates at which methylation levels increased in response to aspartate. IMAGES:

为明确趋化行为（chemotactic behavior）对多位点甲基化（methylation）的依赖程度，研究人员对表达突变型天冬氨酸受体（aspartate receptors）的细菌开展趋化实验：该受体的甲基化位点残基已由谷氨酸（glutamate）突变为天冬氨酸（aspartate）。
实验结果表明，甲基化位点发生突变后细菌趋化功能受损；且快速甲基化位点的突变对趋化的抑制效果，显著强于慢速甲基化位点的突变。在野生型菌株（wild-type strain）中表达该突变受体，仅会对趋化过程产生轻微干扰。体内甲基化实验（in vivo methylation assays）显示，多数突变体的趋化缺陷可归因于其响应天冬氨酸时甲基化水平提升速率的降低。
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