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Budding yeast,and it was found that DNA polymerase and mostly synthesize lagging and leading strands,respectively (Pursell et al. ; Nick McElhinny et al It was initially believed that the two replisomes at sister forks (i.e initiated in the same origin) would behave separately since they travel in opposite directions along template DNA. Even so,it was located that on bacterial circular chromosomes where DNA replication starts from a single defined origin,sister forks move along DNA and usually total DNA replication with related timing at a defined region on the chromosome (Bussiere and Bastia. To explain this coordinated termination of DNA replication,it was proposed that two replisomes at sister forks (sister replisomes) remain attached through DNA replication (Dingman ; Falaschi. This model predicts that template DNA moves into two connected replisomes,and newly replicated sister DNA strands are extruded as replication proceeds. Such DNA motion relative to centrally located stationary replisomes (Lemon and Grossman was indeed confirmed in bacteria Bacillus subtilis and Caulobacter crescentus (Lemon and Grossman ; Jensen et al. ; Migocki et al Additionally,electron microscopy of huge tumor antigen (T antigen) in simian virus ,which functions as a DNA helicase at replication forks (Herendeen and Kelly,showed that unwound DNA from viral replication origins forms two loops that are pinched by the identical pair of associated Tantigen hexamers (Wessel et althus,supporting the associated replisome model. On the other hand,in E. coli,sister replisomes separate shortly following DNA replication initiation and undergo DNA replication independentlyT. Aglafoline Natsume,T.U. Tanaka(Bates and Kleckner ; ReyesLamothe et al In contrast to bacteria and viruses,it remained unknown until not too long ago irrespective of whether sister replisomes are linked with each other in eukaryotes. In budding yeast,livecell imaging was applied to analyze the replication timing of chromosome loci (Fig. (Kitamura et alat which bacteriaderived tetO and lacO arrays have been integrated (Straight et al. ; Michaelis et al These arrays bound TetR and lacI proteins,fused with fluorescent proteins,and were thus visualized as little fluorescent dots. The fluorescent dots increased their intensity upon their DNA replication when the amount of tetO and lacO arrays wasdoubled,which defined their replication timing by microscopy (Kitamura et al Applying this system,two loci had been selected and visualized within a single replicon to ensure that they locate at the opposite sides in the relevant replication origin and show comparable replication timing (based on a genomewide replication timing data: Raghuraman et al. ). Remarkably,these two loci came close to every single other,enhanced their intensity,and subsequently diverged from every other in the course of S phase (Kitamura PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/26698565 et al Such behavior with the two loci suggests that sister replisomes are associated with each other throughout replication with the replicon. Furthermore,inside a separate study,nascent DNA segments were pulselabeled and observed by electron microscopy. This study suggested that human sister replisomes are also associated with every other during DNA replication (Ligasovet alPossible rewards from the association of sister replisomes Why do cells preserve sister replisomes closely connected in the course of replication What positive aspects can cells reap from it One possibility is that the close association enables temporal coordination of DNA replication among sister replisomes. Certainly,such temporal coordination was r.

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