Differential expression and positioning of chemotaxis methylation proteins in Caulobacter

Proteins involved in chemotaxis methylation reactions have been identified in Caulobacter crescentus and their activities, times of synthesis and cellular positions have been determined. The methyl-accepting chemotaxis proteins, the methyl-transferase and the methylesterase were all shown to be active in the flagella-bearing swarmer cell, but all three activities were lost after the swarmer cells shed their flagellum and differentiated into a stalked cell. The membrane methyl-accepting chemotaxis proteins were shown to be synthesized before cell division, coincident with the synthesis of the components of the flagellum, and to be specifically localized in the membrane of the incipient swarmer cell portion of the predivisional cell. The cytoplasmic methylesterase was also found to be differentially synthesized coincident with the period of flagellar biogenesis. Furthermore, methyltransferase activity, present in the predivisional cell, was detected only in the swarmer cell upon cell division. These results demonstrate that the chemotaxis methylation machinery is positionally biased toward one portion of the predivisional cell, and that the time of expression of a set of fla and che genes is correlated with the positioning of their gene products within the cell.