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Mechanism of human Lig1 regulation by PCNA in Okazaki fragment sealing.

ABSTRACT: During lagging strand synthesis, DNA Ligase 1 (Lig1) cooperates with the sliding clamp PCNA to seal the nicks between Okazaki fragments generated by Pol δ and Flap endonuclease 1 (FEN1). We present several cryo-EM structures combined with functional assays, showing that human Lig1 recruits PCNA to nicked DNA using two PCNA-interacting motifs (PIPs) located at its disordered N-terminus (PIPN-term) and DNA binding domain (PIPDBD). Once Lig1 and PCNA assemble as two-stack rings encircling DNA, PIPN-term is released from PCNA and only PIPDBD is required for ligation to facilitate the substrate handoff from FEN1. Consistently, we observed that PCNA forms a defined complex with FEN1 and nicked DNA, and it recruits Lig1 to an unoccupied monomer creating a toolbelt that drives the transfer of DNA to Lig1. Collectively, our results provide a structural model on how PCNA regulates FEN1 and Lig1 during Okazaki fragments maturation.

SUBMITTER: Blair K 

PROVIDER: S-EPMC9767926 | biostudies-literature | 2022 Dec

REPOSITORIES: biostudies-literature

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Mechanism of human Lig1 regulation by PCNA in Okazaki fragment sealing.

Blair Kerry K   Tehseen Muhammad M   Raducanu Vlad-Stefan VS   Shahid Taha T   Lancey Claudia C   Rashid Fahad F   Crehuet Ramon R   Hamdan Samir M SM   De Biasio Alfredo A  

Nature communications 20221220 1

During lagging strand synthesis, DNA Ligase 1 (Lig1) cooperates with the sliding clamp PCNA to seal the nicks between Okazaki fragments generated by Pol δ and Flap endonuclease 1 (FEN1). We present several cryo-EM structures combined with functional assays, showing that human Lig1 recruits PCNA to nicked DNA using two PCNA-interacting motifs (PIPs) located at its disordered N-terminus (PIP<sub>N-term</sub>) and DNA binding domain (PIP<sub>DBD</sub>). Once Lig1 and PCNA assemble as two-stack ring  ...[more]

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