Identification of a Protein Methyltransferase as the cheR Gene Product in the Bacterial Sensing System

Methylation of membrane-bound proteins with apparent molecular weights around 65,000 does not occur in mutants of the generally nonchemotactic cheR class of Salmonella typhimurium. This was shown to be due to the lack of a protein methyltransferase in these mutants by means of an in vitro assay using soluble proteins, membranes, and S-adenosylmethionine as the methyl donor. The methylase from the wild type was purified, characterized, and shown to be of molecular weight 38,000. It is specific for proteins in S. typhimurium and Escherichia coli membranes. The methylase is not required for tumbling but appears to be essential for maintaining the appropriate rate constants and levels of the regulator of the chemotactic response.