AN EXPLANATION FOR LAGGING-STRAND REPLICATION - POLYMERASE HOPPING AMONG DNA SLIDING CLAMPS

The replicase of E. coli, DNA polymerase III holoenzyme, is tightly fa stened to DNA by its ring-shaped beta sliding clamp. However, despite being clamped to DNA, the polymerase must rapidly cycle on and off DNA to synthesize thousands of Okazaki fragments on the lagging strand. T his study shows that DNA polymerase III holoenzyme cycles from one DNA to another by a novel mechanism of partial disassembly of its multisu bunit structure and then reassembly. Upon completing a template, the p olymerase disengages from its beta clamp, hops off DNA, and reassociat es with another beta clamp at a new primed site. The original beta cla mp is left on DNA and may be harnessed by other machineries to coordin ate their action with chromosome replication.