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. 2009 Mar 2;106(12):4647–4652. doi: 10.1073/pnas.0811196106

Fig. 5.

Fig. 5.

Switching mechanism of PCNA binding factors. (A–C) Model switching mechanism proposed in this work. (A) In solution, the DNA ligase adopts various conformations, such as the closed and extended configurations, as observed in the PfuLig and SsoLig crystal structures, respectively. (B) Upon binding to PCNA and DNA, the DNA ligase forms the intermediate crescent configuration, which embraces the DNA. (C) The DNA ligase grips the DNA to accomplish the ligation of nicked DNA, as observed in the crystal structure of hLigI–DNA. Accordingly, the binding sites will be released, thereby enabling the PCNA ring to interact with the PIP-box of the next enzyme. (D) Switching induced by the DNA tilt and swinging-in and -out of the factors bound on the PCNA revolver, proposed in previous works (14, 15, 21, 22). (E) FEN1–PCNA crystal structure, superimposed on the EM map. FEN1 in the X (blue), Y (red), and Z (green) configurations, placed on the free IDCL region of PCNA (yellow).