The primary receptors for aspartate and serine in bacterial chemotaxis have been shown to be the 60,000-dalton proteins encoded by the tar and tsr genes. The evidence is: (i) overproduction of the tar gene product at various levels by recombinant DNA techniques produces proportionate increases in aspartate binding; (ii) aspartate binding copurifies with [3H]methyl-labeled tar gene product; (iii) antibody to tar and tsr protein fragments precipitates a single species of protein (60,000 daltons) which retains binding capacity and [3H]carboxymethyl label. Partially purified tar gene product can be reconstituted into artificial vesicles and retains aspartate binding and aspartate-sensitive methylation and demethylation. These results show that the aspartate and serine receptors are transmembrane proteins of a single polypeptide chain with the receptor recognition site on the outside of the membrane and the covalent methylation site on the inside.

Wang, E. A., & Koshland, D. E. (1980). Receptor structure in the bacterial sensing system. Proceedings of the National Academy of Sciences, 77(12), 7157–7161.