5702 Nucleic Acids Research, 2010, Vol. 38, No. 17 Figure 8. Proposed models of the DNA repair pathways in T. thermophilus HB8. (A) The model of MMR. A DNA mismatch is generated by misincorporation of a base during DNA replication. The MutS/MutL complex recognises the mismatch and nicks the 30- and 50-sides of the incorrect base to create a DNA patch for removal. DNA helicases, such as UvrD, and RecJ or ExoI excise the error-containing patch. DNA polymerase ﬁlls the gap to complete the repair. (B) The model of the repair pathway for deaminated bases. Reactive oxygen species, such as hydroxyl radicals, attack the base to yield deaminated bases. Endonuclease V recognises a deaminated base and hydrolyses the second phosphodiester bond of the 30-side of the bases. A DNA helicase unwinds the chain, and then, ExoI digests the lesion-containing ssDNA. (C) The model of DSB repair. UV-C irradiation causes DSBs in DNA. RecJ processes the termini to the 30-overhanging structure in cooperation with a DNA helicase. The homologous pairing and re-synthesis of the DNA strand yield Holliday junctions. The resolution of Holliday junctions completes the repair.