8v6g
DNA initiation complex (configuration 1) of Xenopus laevis DNA polymerase alpha-primase
Structural highlights
FunctionDPOLA_XENLA Plays an essential role in the initiation of DNA replication. During the S phase of the cell cycle, the DNA polymerase alpha complex (composed of a catalytic subunit POLA1/p180, a regulatory subunit POLA2/p70 and two primase subunits PRIM1/p49 and PRIM2/p58) is recruited to DNA at the replicative forks via direct interactions with MCM10 and WDHD1. The primase subunit of the polymerase alpha complex initiates DNA synthesis by oligomerising short RNA primers on both leading and lagging strands. These primers are initially extended by the polymerase alpha catalytic subunit and subsequently transferred to polymerase delta and polymerase epsilon for processive synthesis on the lagging and leading strand, respectively. The reason this transfer occurs is because the polymerase alpha has limited processivity and lacks intrinsic 3' exonuclease activity for proofreading error, and therefore is not well suited for replicating long complexes (By similarity). Publication Abstract from PubMedThe mechanism by which polymerase alpha-primase (polalpha-primase) synthesizes chimeric RNA-DNA primers of defined length and composition, necessary for replication fidelity and genome stability, is unknown. Here, we report cryo-EM structures of Xenopus laevis polalpha-primase in complex with primed templates representing various stages of DNA synthesis. Our data show how interaction of the primase regulatory subunit with the primer 5' end facilitates handoff of the primer to polalpha and increases polalpha processivity, thereby regulating both RNA and DNA composition. The structures detail how flexibility within the heterotetramer enables synthesis across two active sites and provide evidence that termination of DNA synthesis is facilitated by reduction of polalpha and primase affinities for the varied conformations along the chimeric primer-template duplex. Together, these findings elucidate a critical catalytic step in replication initiation and provide a comprehensive model for primer synthesis by polalpha-primase. A mechanistic model of primer synthesis from catalytic structures of DNA polymerase alpha-primase.,Mullins EA, Salay LE, Durie CL, Bradley NP, Jackman JE, Ohi MD, Chazin WJ, Eichman BF Nat Struct Mol Biol. 2024 May;31(5):777-790. doi: 10.1038/s41594-024-01227-4. , Epub 2024 Mar 15. PMID:38491139[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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