Methylation involved in chemotaxis is regulated during Caulobacter differentiation.

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Abstract
C. crescentus carries a flagellum and is motile only during a limited time in its cell cycle. It was asked if the biochemical machinery that mediates chemotaxis exists coincident with the cell''s structural ability to respond to a chemotactic signal. One function of the chemotaxis machinery, the ability to methylate the carboxyl side chains of a specific set of membrane proteins (methyl-accepting chemotaxis proteins, MCP), is present in C. crescentus. This conclusion is based on the following observations: methionine auxotrophs starved of methionine can swim only in the forward direction (comparable to smooth swimming in the enteric bacteria); a specific set of membrane proteins was found to be methylated in vivo and the incorporated [3H]methyl groups were alkali sensitive; this same set of membrane proteins incorporated methyl groups from S-adenosylmethionine in vitro; and of a total of 8 generally nonchemotactic mutants, 2 were found to swim only in a forward direction and one of these lacked methyltransferase activity. Analysis of in vivo and vitro methylation in synchronized cultures showed that the methylation reaction is lost when the flagellated swarmer cell differentiates into a stalked cell. In vivo methylation reappeared coincident with the biogenesis of the flagellum just prior to cell division. In vitro reconstitution experiments with heterologous cell fractions different cell types showed that swarmer cells contain methyltransferase and their membranes can be methylated. Newly differentiated stalked cells lack methyltransferase activity and membranes from these cells cannot accept methyl groups. MCP methylation is confined to that portion of the cell cycle when flagella are present.