Mechanism of genome instability mediated by human DNA polymerase mu misincorporation.

Pol µ 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 µ results in a promutagenic T:G mispair, leading to genomic instability. Here, crystal structures and kinetics of Pol µ substituting dGTP for dATP on gapped DNA substrates containing templating T were determined and compared. Pol µ 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 µ revealed an unexpected second dGTP in the active site, suggesting its potential mutagenic role among human X family polymerases in NHEJ.

Structural features and functional implications of proteins enabling the robustness of Deinococcus radiodurans.

Deinococcus radiodurans can survive under extreme conditions, including high doses of DNA damaging agents and ionizing radiation, desiccation, and oxidative stress. Both the efficient cellular DNA repair machinery and antioxidation systems contribute to the extreme resistance of this bacterium, making it an ideal organism for studying the cellular mechanisms of environmental adaptation. The number of stress-related proteins identified in this bacterium has mushroomed in the past two decades. The newly identified proteins reveal both commonalities and diversity of structure, mechanism, and function, which impact a wide range of cellular functions. Here, we review the unique and general structural features of these proteins and discuss how these studies improve our understanding of the environmental stress adaptation mechanisms of D. radiodurans.