Editing DNA replication (section)

=== Replication machinery ===

[[File:E. coli replisome.png|thumb|left|E. coli Replisome. Notably, the DNA on lagging strand forms a loop. The exact structure of replisome is not well understood.]]

'''Replication machineries''' consist of factors involved in DNA replication and appearing on template ssDNAs. Replication machineries include primosotors are replication enzymes; DNA polymerase, DNA helicases, DNA clamps and DNA topoisomerases, and replication proteins; e.g. single-stranded DNA binding proteins (SSB). In the replication machineries these components coordinate. In most of the bacteria, all of the factors involved in DNA replication are located on replication forks and the complexes stay on the forks during DNA replication. Replication machineries are also referred to as replisomes, or DNA replication systems. These terms are generic terms for proteins located on replication forks. In eukaryotic and some bacterial cells the replisomes are not formed.{{cn|date=November 2024}}

In an alternative figure, DNA factories are similar to projectors and DNAs are like as cinematic films passing constantly into the projectors. In the replication factory model, after both DNA helicases for leading strands and lagging strands are loaded on the template DNAs, the helicases run along the DNAs into each other. The helicases remain associated for the remainder of replication process. Peter Meister et al. observed directly replication sites in [[budding yeast]] by monitoring [[green fluorescent protein]] (GFP)-tagged DNA polymerases α. They detected DNA replication of pairs of the tagged loci spaced apart symmetrically from a replication origin and found that the distance between the pairs decreased markedly by time.<ref name="in&out">{{Cite journal |vauthors=Meister P, Taddei A, Gasser SM |date=June 2006 |title=In and out of the replication factory |journal=Cell |volume=125 |issue=7 |pages=1233–5 |doi=10.1016/j.cell.2006.06.014 |pmid=16814710 |s2cid=15397410 |doi-access=free}}</ref> This finding suggests that the mechanism of DNA replication goes with DNA factories. That is, couples of replication factories are loaded on replication origins and the factories associated with each other. Also, template DNAs move into the factories, which bring extrusion of the template ssDNAs and new DNAs. Meister's finding is the first direct evidence of replication factory model. Subsequent research has shown that DNA helicases form dimers in many eukaryotic cells and bacterial replication machineries stay in single intranuclear location during DNA synthesis.<ref name="watson237">{{Cite book |title=Molecular Biology of the Gene |vauthors=Watson JD, Baker TA, Bell SP, Gann A, Levine M, Losick R, Inglis CH |date=2008 |publisher=Pearson/Benjamin Cummings |isbn=978-0-8053-9592-1 |edition=6th |location=San Francisco |page=237}}</ref>

Replication Factories Disentangle Sister Chromatids. The disentanglement is essential for distributing the chromatids into daughter cells after DNA replication. Because sister chromatids after DNA replication hold each other by '''[[Cohesin]]''' rings, there is the only chance for the disentanglement in DNA replication. Fixing of replication machineries as replication factories can improve the success rate of DNA replication. If replication forks move freely in chromosomes, catenation of nuclei is aggravated and impedes mitotic segregation.<ref name="in&out" />