Initiation of replication at oric DnaA 9-mers TP DnaC DnaB (helicase】 Open Initial complex ATP complex 13-mers Negatively supercoiled template Prepriming complex DnaB ● Dnaa binds and begins to melt double helix Helicase (DnaB)continues to separate strands
Initiation of replication at oriC • DnaA binds and begins to melt double helix • Helicase (DnaB) continues to separate strands
Two other factors participate in open complex formation at oric 1.RNA polymerase The role of RNA polymerase seems to be to synthesize a short piece of RNA that creates an R loop.The R loop can be adjacent to oriC,rather than within it. 2.HU protein This is a small basic DNA-binding protein that can induce bending in double- stranded DNA.This bending,together with the R loop,presumably destabilizes the DNA double helix and facilitates melting of the DNA to form the open complex
Two other factors participate in open complex formation at oriC 1.RNA polymerase The role of RNA polymerase seems to be to synthesize a short piece of RNA that creates an R loop．The R loop can be adjacent to oriC，rather than within it． 2.HU protein This is a small basic DNA-binding protein that can induce bending in doublestranded DNA．This bending，together with the R loop，presumably destabilizes the DNA double helix and facilitates melting of the DNA to form the open complex．
Finally,DnaB stimulates the binding of the primase(DnaG),completing the primosome.The primosome remains with the replisome as it carries out elongation,and serves at least two functions. First,it must operate repeatedly in priming Okazaki fragment synthesis to build the lagging strand. Second,DnaB serves as the helicase that unwinds DNA to provide templates for both the leading and lagging strands
Finally,DnaB stimulates the binding of the primase(DnaG)，completing the primosome．The primosome remains with the replisome as it carries out elongation，and serves at least two functions． First，it must operate repeatedly in priming Okazaki fragment synthesis to build the lagging strand． Second，DnaB serves as the helicase that unwinds DNA to provide templates for both the leading and lagging strands．
Copyright The McGraw-Hill Companies,Inc.Permission required for reproduction or display. 9 mers HU ATP.dnaA 38 5 mM ATP 13 mers OriC 209 389 Bgl ll dnaB dnac ATP INITIAL OPEN COMPLEX COMPLEX SUPERCOILED TEMPLATE PRIMING AND REPLICATION PREPRIMING COMPLEX (Source:DNA Replication,2/e.(plate 15)by Arthur Komberg and Tania Baker1992 by W.H.Freeman and Company.Used with permission