Lack of sugar discrimination by human Pol mu requires a single glycine residue |
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Authors: | Ruiz José F Juárez Raquel García-Díaz Miguel Terrados Gloria Picher Angel J González-Barrera Sergio Fernández de Henestrosa Antonio R Blanco Luis |
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Institution: | José F. Ruiz, Raquel Juárez, Miguel García-Díaz, Gloria Terrados, Angel J. Picher, Sergio González-Barrera, Antonio R. Fernández de Henestrosa, and Luis Blanco |
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Abstract: | DNA polymerase mu (Pol µ) is a novel family X DNA polymerase that has been suggested to play a role in micro-homology mediated joining and repair of double strand breaks. We show here that human Pol µ is not able to discriminate against the 2′-OH group of the sugar moiety. It inserts rNTPs with an efficiency that is <10-fold lower than that of dNTPs, in sharp contrast with the >1000-fold discrimination characteristic of most DNA-dependent DNA polymerases. The lack of sugar discrimination by Pol µ is demonstrated by its ability to add rNTPs to both DNA and RNA primer strands, and to insert both deoxy- and ribonucleotides on growing nucleic acid chains. 3D-modelling of human Pol µ based on the available Pol β and TdT structural information allowed us to predict candidate residues involved in sugar discrimination. Thus, a single amino acid substitution in which Gly433 residue of Pol µ was mutated to the consensus tyrosine present in Pol β, produced a strong increase in the discrimination against ribonucleotides. The unusual capacity to insert both rNTPs and dNTPs will be discussed in the context of the predicted roles of Pol µ in DNA repair. |
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