Whither the replisome Emerging perspectives on the dynamic nature of the DNA replication machinery

Replisomes were originally thought to be multi-protein machines with a stabile and defined structure during replication. Discovery that replisomes repeatedly discard sliding clamps and assemble a new clamp to start each Okazaki fragment provided the first hint that the replisome structure changes during replication. Recent studies reveal that the replisome is more dynamic than ever thought possible. Replisomes can utilize many different polymerases; the helicase is regulated to travel at widely different speeds; leading and lagging strands need not always act in a coupled fashion with DNA loops; and the replication fork does not always exhibit semi-discontinuous replication. We review some of these findings here and discuss their implications for cell physiology as well as enzyme mechanism.