Productive interaction between the chromosome partitioning proteins, ParA and ParB, is required for the progression of the cell cycle in Caulobacter crescentus

Abstract

SummaryIn Caulobacter crescentus the partitioning proteins ParA and ParB operate a molecular switch that couples chromosome partitioning to cytokinesis. Homologues of these proteins have been shown to be important for the stable inheritance of F-plasmids and the prophage form of bacteriophage P1. In C. crescentus , ParB binds to sequences adjacent to the origin of replication and is required for the initiation of cell division. Additionally, ParB influences the nucleotidebound state of ParA by acting as a nucleotide exchange factor. Here we have performed a genetic analysis of the chromosome partitioning protein ParB. We show that C. crescentus ParB, like its plasmid homologues, is composed of three domains: a carboxyl-terminal dimerization domain; a central DNA-binding, helix-turn-helix domain; and an aminoterminal domain required for the interaction with ParA. In vivo expression of amino-terminally deleted parB alleles has a dominant lethal effect resulting in the inhibition of cell division. Fluorescent in situ hybridization experiments indicate that this phenotype is not caused by a chromosome partitioning defect, but by the reversal of the amounts of ATPversus ADP-bound ParA inside the cell. We present evidence suggesting that amino-terminally truncated and full-length, wild-type ParB form heterodimers which fail to interact with ParA, thereby reversing the intracellular ParA-ATP to ParA-ADP ratio. We hypothesize that the amino-terminus of ParB is required to regulate the nucleotide exchange of ParA which, in turn, regulates the initiation of cell division.

Replication initiator DnaA binds at the Caulobacter centromere and enables chromosome segregation

“…4A, referred here as parS + ). This chromosomal region serves as a protein hub where the segregation machinery and additional interacting factors contribute to the temporal and spatial control of chromosome segregation (8,9,19,20,22,27). Because DnaA is known to bind ori to enable replication initiation (28), we considered the possibility that DnaA binds directly to the parS centromere region to activate ParB/parS translocation.…”

Towards understanding the molecular basis of bacterial DNA segregation

“…The N-terminal region of ParB of C. crescentus, like that of plasmid P1 ParB and F plasmid SopB, is the determinant for interaction with ParA (Figge et al 2003).…”

Getting in the Loop: Regulation of Development inCaulobacter crescentus

“…When the parS sequence is moved elsewhere on the chromosome, chromosome segregation does not begin until DNA replication has reached the parS sequence (252), indicating that parS functions as a bacterial equivalent of a eukaryotic centromere. ParB binds to parS in a sequence-specific fashion and has three domains: an N-terminal ParA interaction domain, a middle DNA binding domain, and a C-terminal dimerization domain (60). While it has been known for some time that ParA has ATPase activity, only recently has it been found to form filaments in E. coli (54).…”