Mizuno T, Imae Y
J Bacteriol. 1984 Jul;159(1):360-7. doi: 10.1128/jb.159.1.360-367.1984.
Mutants in Escherichia coli having defects in one of the methyl-accepting chemotaxis proteins, Tsr protein, which is the chemoreceptor and transducer for L-serine, showed a reduced but similar type of thermoresponse compared with wild-type strains; the cells showed smooth swimming upon temperature increase and tumbling upon temperature decrease. However, when the mutant cells were adapted to attractants such as L-aspartate and maltose, which are specific to another methyl-accepting chemotaxis protein, Tar protein, the direction of the thermoresponse was found to be inverted; a temperature increase induced tumbling and a temperature decrease induced smooth swimming. Consistent with this, the mutant cells showed inverted changes in the methylation level of Tar protein upon temperature changes. Wild-type strains but not Tar protein-deficient mutants exhibited the inverted thermoresponse when the cells were simultaneously adapted to L-aspartate and L-serine, indicating that Tar protein has a key role in the inversion of the thermoresponse. Thus, besides Tsr protein, Tar protein has a certain role in thermoreception. A simple model for thermoreception and inversion of the thermoresponse is also discussed.
大肠杆菌中甲基接受趋化蛋白之一Tsr蛋白存在缺陷的突变体，Tsr蛋白是L-丝氨酸的化学感受器和转导器，与野生型菌株相比，其热反应类型有所降低但相似；细胞在温度升高时表现出平滑游动，在温度降低时表现出翻滚。然而，当突变细胞适应诸如L-天冬氨酸和麦芽糖等吸引剂时，这些吸引剂是另一种甲基接受趋化蛋白Tar蛋白所特有的，发现热反应的方向发生了反转；温度升高诱导翻滚，温度降低诱导平滑游动。与此一致的是，突变细胞在温度变化时Tar蛋白的甲基化水平发生了反转变化。当细胞同时适应L-天冬氨酸和L-丝氨酸时，野生型菌株而非Tar蛋白缺陷型突变体表现出反转的热反应，这表明Tar蛋白在热反应的反转中起关键作用。因此，除了Tsr蛋白外，Tar蛋白在热感受中也有一定作用。还讨论了热感受和热反应反转的简单模型。
