DNA 複製

DNA replication steps are as follows: binding to initiation site, unwinding dsDNA(double stranded DNA), holding ssDNA(single stranded DNA), preventing supercoiling, priming with hnRNA, elongation by polymerase, proofreading, removing the primer, combining fragments, and rewinding ssDNA. Replication rates are 750-1000 bp in bacteria, 50-100 bp in eukaryotes. In prokaryote DNA synthesis, the replication starts with 20-40 DnaA (52 kMr, tetramer) binding to oriC(origin of replication) site, which requires ATP and HU. Helicase(DnaB, 300 kMr, hexamer) and DnaC complex unwinds dsDNA, which also requires ATP. DnaC is released by DnaT, and SSBs(single stranded DNA-binding protein, tetramer) holds ssDNA from winding. Primase(DnaG, 60 kMr) synthesizes hnRNA, the first DNA sequence. Primase, helicase, DnaT and PriA/B/C form primosome. The complementary DNA sequences are synthesized by polymerase III(DnaE, 1 MMr, 10 subunits, dimer). Subunit ; ϵ; forms the core which is dimerized by subunit, while as forms sliding clamp, and ; ; ′; ; subunits plays a role in clamp loading. At the leading strand, one consecutive DNA sequence is synthesized, and at the lagging strand Okazaki fragments(1- 5 kbp) are synthesized. The primer sequence of the fragments are removed by polymerase I(3 subunits), and combined by DNA ligase. Polymerase I contains 5'-3' exonuclease and polymerase which ``translate nicks'', i.e. relocate nicks. Polymerase III and primosome form replisome. The DNA sequence polymerized from NTP, removing triphosphate. Polymerase II proofread the DNA. Topoisomerase I loosens supercoiling by cleaving single stranded DNA, while topoisomerase II(gyrase) cleaves double stranded DNA. subunit of gyrase cleaves dsDNA whereas subunit is a ATPase. At termination site(ter sequence) the replication ends by binding to Ter(ter binding protein). In the case of phase infected E.coli, initiation starts with O protein binding to ori. P protein and dnaB protein binds to O protein. Deassociation of P protein by dnaK, dnaJ, and GrpE activates dnaB helicase. In eukaryotes, DNA polymerase corresonds prokaryote DNA polymerase I and replicates DNA at the lagging strand. DNA polymerase repair the sequence, DNA polymerase corresponds to prokaryote DNA polymerase III. DNA polymerase ϵ corresponds to prokaryote DNA polymerase II and repairs the DNA sequence. DNA polymerase replicates mitochondria DNA.