Dynamics of human replication factors in the elongation phase of DNA replication

In eukaryotic cells, DNA replication is carried out by coordinated actions of many proteins, including DNA polymerase delta (pol delta), replication factor C (RFC), proliferating cell nuclear antigen (PCNA) and replication protein A. Here we describe dynamic properties of these proteins in the elongation step on a single-stranded M13 template, providing evidence that pol delta has a distributive nature over the 7 kb of the M13 template, repeating a frequent dissociation-association cycle at growing 3'-hydroxyl ends. Some PCNA could remain at the primer terminus during this cycle, while the remainder slides out of the primer terminus or is unloaded once pol delta has dissociated. RFC remains around the primer terminus through the elongation phase, and could probably hold PCNA from which pol delta has detached, or reload PCNA from solution to restart DNA synthesis. Furthermore, we suggest that a subunit of pol delta, POLD3, plays a crucial role in the efficient recycling of PCNA during dissociation-association cycles of pol delta. Based on these observations, we propose a model for dynamic processes in elongation complexes.