Regulation of flagellin synthesis in the cell cycle of Caulobacter: Dependence on DNA replication

Abstract

Synthesis of the two filament proteins (flagellin A and flagellin B) of the Caulobacter crescentus flagellum was measured during the cell cycle. Synchronous cells were pulse-labeled with 35S-methionine, and flagellin proteins were isolated from crude extracts by radioimmune precipitation. The results showed that both proteins are maximally induced during the G2 period and that their induction requires de novo transcription. Flagellin A, however, continues to be made in the progeny swarmer cells after flagellin B synthesis has stopped. This discoordination in flagellin A and B synthesis and the relative abundance of the two proteins may result in part from the longer functional half-life of the flagellin A messenger RNA. Analysis of temperature-sensitive DNA chain elongation mutants suggests that the periodicity of flagellin A and B synthesis in the cell cycle is controlled by a late cell cycle event, presumably the completion of chromosome replication.