“Background Bacterial genomes appear as compact DNA masses

“Background Bacterial genomes appear as compact DNA masses, termed nucleoids, located centrally along both the length and width of the cells [1]. Nucleoids are highly organised structures within which each chromosome region occupies Selleck Luminespib specific locations along the length of the cell and displays a distinct choreography selleck screening library during the cell cycle (for reviews: [2,

3]). In most bacteria, nucleoids contain a single chromosome replicated from a single origin. This defines two oppositely oriented replichores, each extending from the replication origin, oriC to the terminal (ter) region, oppositely located on circular chromosomes. This replicative organisation has important consequences for the global organisation and segregation of bacterial nucleoids. In E. coli, replication occurs around the cell centre (i.e., the mid-cell position) [4]. Segregation is concomitant with replication so that replicated loci are segregated from mid-cell to the equivalent positions in the future daughter cells (the quarter positions) following the order of their replication [5–9]. The oriC region (ori) is thus the first to segregate, and the ter region the last. In newborn

cells, loci of the ter region are located close to the new cell pole (polar positioning) and migrate towards the midcell during the replication process. Recent advances Fosbretabulin mouse in bacterial cell cytology allow a general model of the check details E. coli nucleoid structure to be established. The ori region, located towards midcell, migrates to the quarter positions after being duplicated. The two replichores occupy distinct locations on each side of ori with chromosome loci recapitulating the ori-ter genetic map along the cell length axis [7, 10, 11]. In this model, the ter region is inferred to contain a stretched

region linking the two nucleoid edges [12, 13]. This linking region is believed to be composed of a segment of 50 kb randomly taken within the 400 kb ter region. Notably, the ter region is the site of specific activities involved in segregation [14, 15]: in particular, it interacts with the MatP protein [16] and with the FtsK DNA translocase ([17]; our unpublished results). In addition to this replichore organisation, the E. coli nucleoid appears to be structured into macrodomains (MDs). MDs are 0.5 to 1 Mb regions inferred to be self-compacted and composed of loci having similar intracellular positioning and dynamics during segregation [6, 9, 18]. The E. coli chromosome contains four MDs: the Ori and Ter MDs (containing ori and ter, respectively) and the Right and Left MDs flanking the Ter MD. The two regions flanking the Ori MD, called the non-structured regions (NS regions), do not display MD properties and contain loci displaying a higher intracellular mobility than MD-borne loci [9]. Most studies of the localization of chromosomal loci in bacteria have focused on their position along the length of the cell.

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