Aberrant Regulation of Methylesterase Activity in CheD Chemotaxis Mutants of Escherichia Coli

The adaptation process in several cheD chemotaxis mutants, which carry defects in tsr, the serine transducer gene, was examined. cheD mutants are smooth swimming and generally nonchemotactic; the defect is dominant to the wild-type tsr gene (J. S. Parkinson, J. Bacteriol. 142:953-961, 1980). All classes of methyl-accepting chemotaxis proteins synthesized in unstimulated cheD strains are overmethylated relative to the wild type. We found that the steady-state rate of demethylation in cheD mutants was low; this may explain their overmethylated phenotype. In addition, all cheD mutants showed diminished responsiveness of methylesterase activity to attractant and repellent stimuli transduced by either the Tsr or Tar protein, and they did not adapt. These results suggest that the dominant nature of the cheD mutations is manifested as a general defect in the regulation of demethylation. Some of these altered properties of methylesterase activity in cheD mutants were exhibited in wild-type cells that were treated with saturating concentrations of serine. The mutant Tsr protein thus seems to be locked into a signaling mode that suppresses tumbling and inhibits methylesterase activity in a global fashion. We found that the Tar and mutant Tsr proteins synthesized in cheD strains were methylated and deamidated at the correct sites and that the mutations were not located in the methylated peptides. Thus, the signaling properties of the transducers may be controlled at sites distinct from the methyl-accepting sites.