title: Light-dependent and asynchronous replication of  cyanobacterial multi-copy chromosomes.
abstract: While bacteria such as Escherichia coli and Bacillus subtilis harbour a single circular chromosome, some freshwater cyanobacteria have multiple chromosomes p er cell. The detailed mechanism(s) of cyanobacterialreplication remains unclear. To elucidate the replication origin (ori ), form and synchrony of the multi-copy genome in freshwater cyanobacteria Synechococcus elongatus PCC 7942 we constructed strain S. 7942TK that can incorporate 5-bromo-2'- deoxyuridine (BrdU) into genomic DNA and analysed its de novo DNA synthesis. The uptake of BrdU was blocked under dark and resumed after transfer of the culture to light conditions. Mapping analysis of nascent DNA fragments using a next-generation sequencer indicated that replication starts bidirectionally from a single ori, which locates in the upstream region of the dnaN gene. Quantitative analysis of BrdU-labelled DNA and whole-genome sequence analysis indicated that the peak timing of replication precedes that of cell division and that replication is initiated asynchronously not only among cell populations but also among the multi-copy chromosomes. Our findings suggest that replication initiation is regulated less stringently in S. 7942 than in E. coli and B. subtilis.
authors.affiliation: Department of Bioscience and 2Genome Research Center, Tokyo University of Agriculture, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Watanabe
authors.forename: Ryudo
authors.initials: R
authors.lastname: Ohbayashi
authors.forename: Yuh
authors.initials: Y
authors.lastname: Shiwa
authors.forename: Aska
authors.initials: A
authors.lastname: Noda
authors.forename: Yu
authors.initials: Y
authors.lastname: Kanesaki
authors.forename: Taku
authors.initials: T
authors.lastname: Chibazakura
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Yoshikawa
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D001973:Bromodeoxyuridine / Q000378:metabolism; D002876:Chromosomes, Bacterial / Q000378:metabolism*; D042522:DNA Replication Timing; D004269:DNA, Bacterial / Q000096:biosynthesis; D004259:DNA-Directed DNA Polymerase / Q000235:genetics; D003624:Darkness; D008027:Light; D018741:Replication Origin; D017422:Sequence Analysis, DNA; D013194:Staining and Labeling / Q000379:methods; D046940:Synechococcus / Q000502:physiology* / Q000528:radiation effects
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004259:DNA-Directed DNA Polymerase; C083980:dnaN protein, Bacteria; D001973:Bromodeoxyuridine