Bacterial tumble regulator may be inactivated by methylation

Abstract

KORT et al.¹ have described the methylation of a membrane protein which seems to be involved in bacterial chemotaxis: they show that addition of attractants affects the methylation, that the source of the methyl group is methionine, a compound required for chemotaxis, and that certain non-chemotactic mutants fail to carry out the methylation reaction. There is no relationship, however, between the amount of methylation and the tumble frequency, and the exact role of this methylation, therefore, remains mysterious. Control of the tumbling process is essential for chemotaxis; peritrichous bacteria swim in short straight-line runs that are separated by abrupt changes of direction (tumbles). In the presence of attractants, however, the tumbling frequency either decreases or increases as the bacterium swims up or down the concentration gradient, respectively². Runs are due to counterclockwise rotation of the flagella, whereas clockwise rotation causes tumbling³. Aswad and Koshland⁴ have proposed the existence of a “tumble-regulating substance” that would control the direction of the rotation: clockwise rotation of the flagella (and therefore tumbling of the bacteria) occurring when the concentration of this regulating substance falls below a certain threshold. The same authors have suggested that S-adenosyl-methionine, the product of the reaction of one molecule of methionine with one molecule of ATP⁵, might be necessary for the degradation of the tumble regulator. I propose that the methylated protein described by Kort et al.¹ may be the inactivated tumble regulator.