Phosphorylation of the Caulobacter Cell Cycle Regulator CtrA by Two Essential Kinases

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The bacterium Caulobacter crescentus exists as two distinct cell types, motile swarmer cells and stationary stalked cells. Each time Caulobacter divides, one cell of each type is produced, in a process called asymmetric cell division. The swarmer cell is incapable of chromosome replication and cell division. In order to divide, the swarmer cell must first differentiate into a stalked cell that can initiate chromosome replication. Asymmetric cell division and differentiation of one cell type into another are fundamental processes in the development of all higher organisms, and Caulobacter provides a relatively simple model system in which to study them in detail. A network of signal transduction proteins called two-component proteins orchestrates the complex Caulobacter life cycle. Research in the Ryan lab focuses on CtrA, a two-component protein that regulates the cell cycle by affecting the transcription of multiple genes. CtrA must be active to promote the transcription of genes involved in cell division, but earlier in the cell cycle CtrA must be inactive, because it also blocks the initiation of chromosome replication. The goal of this project is to determine how two essential kinases, CckA and DivL, activate CtrA by phosphorylation only at the correct times during the cell cycle. The educational component of this project is a summer laboratory course for undergraduates in which each student will disrupt a previously unstudied Caulobacter gene and characterize the resulting mutant phenotype. Students will learn basic techniques in molecular biology and genetics while making original contributions in microbiology.