Abstract
Control of chromosome replication involves a common set of regulators in eukaryotes, whereas bacteria with divided genomes use chromosome-specific regulators. How bacterial chromosomes might communicate for replication is not known. In Vibrio cholerae, which has two chromosomes (chrI and chrII), replication initiation is controlled by DnaA in chrI and by RctB in chrII. DnaA has binding sites at the chrI origin of replication as well as outside the origin. RctB likewise binds at the chrII origin and, as shown here, to external sites. The binding to the external sites in chrII inhibits chrII replication. A new kind of site was found in chrI that enhances chrII replication. Consistent with its enhancing activity, the chrI site increased RctB binding to those chrII origin sites that stimulate replication and decreased binding to other sites that inhibit replication. The differential effect on binding suggests that the new site remodels RctB. The chaperone-like activity of the site is supported by the finding that it could relieve the dependence of chrII replication on chaperone proteins DnaJ and DnaK. The presence of a site in chrI that specifically controls chrII replication suggests a mechanism for communication between the two chromosomes for replication.
Highlights
Eukaryotes invariably have many chromosomes, whereas one chromosome is the norm in bacteria
Genome maintenance in dividing cells requires that the chromosomes replicate reliably once per cell cycle, and that this replication be timed to allow for proper segregation of the daughter chromosomes before cell division
We provide evidence that a site in chromosome I can control the frequency and timing of replication of chromosome II
Summary
Eukaryotes invariably have many chromosomes, whereas one chromosome is the norm in bacteria. The bacteria with a multipartite genome have one main chromosome containing most of the housekeeping genes [2]. Replication of this chromosome, which is analogous to the chromosome of monochromosome bacteria, is controlled by the initiator protein, DnaA. DnaA is well-conserved in bacteria and has structural homology to eukaryotic initiators, Cdc and Orc proteins [3,4]. Plasmids often use DnaA as a replication factor, they do not depend on it to control their copy number; this is accomplished by initiators that they encode themselves. Bacteria with multipartite genomes differ from eukaryotes in that eukaryotic regulators of replication are not chromosome-specific [8]
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