Mechanism of genome instability mediated by human DNA polymerase mu misincorporation

Pol mu is capable of performing gap-filling repair synthesis in the nonhomologous end joining (NHEJ) pathway. Together with DNA ligase, misincorporation of dGTP opposite the templating T by Pol mu results in a promutagenic T:G mispair, leading to genomic instability. Here, crystal structures and kinetics of Pol mu substituting dGTP for dATP on gapped DNA substrates containing templating T were determined and compared. Pol mu is highly mutagenic on a 2-nt gapped DNA substrate, with T:dGTP base pairing at the 3' end of the gap. Two residues (Lys438 and Gln441) interact with T:dGTP and fine tune the active site microenvironments. The in-crystal misincorporation reaction of Pol mu revealed an unexpected second dGTP in the active site, suggesting its potential mutagenic role among human X family polymerases in NHEJ. Pol mu performs gap-filling repair synthesis in the nonhomologous end joining (NHEJ) pathway. Here the authors provide crystal structures and kinetics of human Pol mu to reveal insights into the molecular mechanism of Pol mu during the process of dGTP misincorporation.

Automated summary

Pol mu can perform gap-filling repair synthesis in NHEJ and has a mutagenic role under certain conditions. Crystal structures and kinetics of Pol mu reveal insights into its molecular mechanism during dGTP misincorporation, with two residues playing a crucial role in the active site microenvironment.