UCLA

The coordination of essential cell cycle events is necessary to maintain the viability of a species over many generations; two core processes to any replicative cell is the duplication of chromosomal DNA and the division of a growing cell into two functional daughters. The crescent-shaped α-proteobacteria, Caulobacter crescentus, has a distinct biphasic life cycle making it ideal to study such cell cycle linked events. The core protein of cell division in C. crescentus is the essential, and highly conserved tubulin-homologue, FtsZ. Prior to FtsZ directed cell division, duplicating chromosomes are quickly sequestered to opposing regions of the replicative cell such that each daughter will contain a complete chromosome after division. The three-component partitioning complex, ParAB/parS, is homologous to plasmid segregation systems and essential to the viability of C. crescentus. Previous work has shown that changes to the cellular levels of partitioning complex proteins have a drastic effect on the cell cycle, including the loss of FtsZ ring structures associated with cell division. Using a biochemical approach with purified protein components, the interplay between the partitioning complex proteins and cytokinetic protein FtsZ was addressed. The work presented in this dissertation clearly demonstrates the ability of the partitioning complex to directly regulate FtsZ assembly. The data shows that the ATP-bound form of ParA is a potent stimulator of FtsZ assembly and capable of lowering the critical concentration of FtsZ required for filamentation. Additionally, ParA seems capable of changing the nature of assembled FtsZ, causing an overall elongation of filaments and inducing distinct curvatures into their structure. ParA is a member of a superfamily of ATPase proteins, which comprises two known negative regulators of FtsZ filamentation. It is therefore proposed that ParA is a physiologically relevant activator of FtsZ assembly based on previous cytological results, the relation of ParA to known FtsZ regulators and biochemical results presented within this work. The activation of FtsZ assembly by the partitioning protein ParA is a novel example of stimulatory FtsZ regulation by an essential and active participant in a core, chromosomally linked process.