Proteins at work at the replication fork
The replisome and accessory proteins carry out a number of steps at the replication fork. Topoisomerase and helicase unwind and open the double helix in preparation for DNA replication. When the double helix has been unwound, single-strand-binding proteins prevent the double helix from re-forming. The illustration is a representation of the so-called trombone model (named for its resemblance to a trombone owing to the looping of the lagging strand) showing how the two catalytic cores of the replisome are envisioned to interact to coordinate the numerous events of leading- and lagging-strand replication.

ANIMATED ART: Leading- and lagging-strand synthesis