Characterization of a coupled DNA replication and translesion synthesis polymerase supraholoenzyme from archaea.

The ability of the replisome to seamlessly coordinate both high fidelity and translesion DNA synthesis requires a means to regulate recruitment and binding of enzymes from solution. Co-occupancy of multiple DNA polymerases within the replisome has been observed primarily in bacteria and is regulated by post-translational modifications in eukaryotes, and both cases are coordinated by the processivity clamp. Because of the heterotrimeric nature of the PCNA clamp in some archaea, there is potential to occupy and regulate specific polymerases at defined subunits. In addition to specific PCNA and polymerase interactions (PIP site), we have now identified and characterized a novel protein contact between the Y-family DNA polymerase and the B-family replication polymerase (YB site) bound to PCNA and DNA from Sulfolobus solfataricus. These YB contacts are essential in forming and stabilizing a supraholoenzyme (SHE) complex on DNA, effectively increasing processivity of DNA synthesis. The SHE complex can not only coordinate polymerase exchange within the complex but also provides a mechanism for recruitment of polymerases from solution based on multi-equilibrium processes. Our results provide evidence for an archaeal PCNA 'tool-belt' recruitment model of multienzyme function that can facilitate both high fidelity and translesion synthesis within the replisome during DNA replication.