This schematic diagram shows a current view of the arrangement of replication proteins at a replication fork when DNA is being synthesized. The lagging-strand DNA has been folded to bring the lagging-strand DNA polymerase molecule into a complex with the leading-strand DNA polymerase molecule. This folding also brings the 3' end of each completed Okazaki fragment close to the start site for the next Okazaki fragment. Because the lagging-strand DNA polymerase molecule remains bound to the rest of the replication proteins, it can be reused to synthesize successive Okazaki fragments. In this diagram, it is about to let go of its completed DNA fragment and move to the RNA primer that will be synthesized nearby, as required to start the next DNA fragment. Additional proteins (not shown) help to hold the different protein components of the fork together, enabling them to function as a well-coordinated protein machine. ) h# D* Q4 H. f. C& J[attach]37617[/attach] 9 N& b. n- A' u8 m% h8 i8 `Sliding clamp: this clamp keeps the polymerase firmly on the DNA when it is moving , but relases it as soon as the polymerase runs into a double-strand region of DNA. 1 {( t3 T# ?- m# b+ C, N# q/ P; R- |7 D& C
Clamp loader: the assembly of the clamp around the DNA requires ATP hydrolysis by a special pratein complex, the clamp loaer, which hydrolyze ATP as it loads the clamp on to a primer-template junction. 1 ?3 \6 b2 O. A5 {7 ?- V& ?. P[attach]37617[/attach]作者: chleiwu 时间: 2012-1-9 22:39