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

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) and DNA binding domain (PIP). Once Lig1 and PCNA assemble as two-stack rings encircling DNA, PIP is released from PCNA and only PIP is required for ligation to facilitate the substrate handoff from FEN1.

Structure and mechanism of action of the BRCA2 breast cancer tumor suppressor.

Mutations in BRCA2 increase susceptibility to breast, ovarian and prostate cancers. The product of human BRCA2, BRCA2 protein, has a key role in the repair of DNA double-strand breaks and interstrand cross-links by RAD51-mediated homologous recombination. Here, we present a biochemical and structural characterization of full-length (3,418 amino acid) BRCA2, alone and in complex with RAD51.