Practice question

Eukaryotic replicative polymerases delta and epsilon are intrinsically poorly processive adding only tens of nucleotides per binding. Processivity depends on circular trimeric protein PCNA, proliferating cell nuclear antigen, that completely encircles duplex DNA forming sliding clamp. Loaded by RFC clamp loader using ATP hydrolysis, PCNA slides freely and tethers polymerase via PIP-box interaction preventing dissociation. It dramatically increases synthesis from tens to thousands of nucleotides processively. PCNA also coordinates Okazaki maturation, mismatch repair, translesion synthesis serving as central replication hub analogous to bacterial beta clamp dimer.