Project description:We searched for regulators of chromosome replication in the cell cycle model Caulobacter crescentus and found a novel DNA-binding protein that selectively aids both the initiation of chromosome replication and the initial steps of chromosome partitioning. We identified and purified a protein (OpaA) that binds the chromosome origin of replication (Cori) and its higher-affinity binding to mutated Cori-DNA that increases Cori-plasmid replication in vivo. opaA gene expression is essential for normal growth and sufficient OpaA levels are required for the correct timing of chromosome replication. Whole genome ChIP-seq identified dynamic DNA-binding distributions for OpaA, with the strongest associations at the partitioning (parABS) locus near Cori. Using molecular-genetic and fluorescence microscopy experiments, we showed that OpaA also promotes the first steps of chromosome partitioning, the initial separation of the duplicated parS loci following Cori replication. This separation occurs before the parABS-dependent partitioning and it coincides with the poorly defined mechanism(s) that establishes chromosome asymmetry: C. crescentus chromosomes are partitioned to distinct cell-poles which develop into replicating and non-replicating cell-types. We propose that OpaA coordinates chromosome replication with asymmetry-establishing chromosome separation, noting that both roles are consistent with the phylogenetic restriction of opaA to asymmetrically dividing bacteria that avoid multi-fork replication.
Project description:Goal: We have discovered and charactherized a new Nucleoid Associated Protein in Caulobacter crescentus, that we named RedN. To determine its global binding on C.crescentus chromosome we have performed a ChIP-seq using a strain with a RedN-Venus fusion expressed at gene loci and as single copy on the chromosome.
Project description:High-resolution mapping of the spatial organization of Caulobacter crescentus chromosome by chromosome conformation capture in conjunction with next-generation sequencing (Hi-C)
Project description:The Escherichia coli nucleoid is confined within a rod shaped cell many times smaller than the outstretched chromosome. While extensive compaction is necessary for this process, the chromosome must at the same time remain accessible to essential cellular processes such as replication and transcription. Currently, the individual contributions of cellular confinement, chromosome topology, replication and transcription on nucleoid organization are not well understood. Here we synchronize E. coli cells in stationary phase, where replication has ceased, each cell contains only one copy of the chromosome, and transcription is minimal. We then release the cells and capture chromosome contacts and transcription immediately following release and through-out one cell cycle. Polymer models of confined and topologically constrained circular polymers revealed that cellular confinement and topology do not contribute extensively to the organization of the E. coli nucleoid. Rather, local nucleoid structure is established concurrent with replication, and higher order organization is formed by the replication dependant clustering of linearly distant SeqA bound sites and cell cycle specific gene transcription.
