Generation, repair and replication of guanine oxidation products

Guanine is the most readily oxidized of the four DNA bases, and guanine oxidation products cause G:C-T: A and G: C-C: G transversions through DNA replication. 8-Oxo-7,8-dihydroguanine (8-oxoG) causes G: C-T: A transversions but not G: C-C: G transversions, and is more readily oxidized than guanine. This review covers four major findings. (i) 2,2,4-Triamino-5(2H)oxazolone (Oz) is produced from guanine and 8-oxoG under various oxidative conditions. Guanine is incorporated opposite Oz by DNA polymerases, except REV1. (ii) Several enzymes exhibit incision activity towards Oz. (iii) Since the redox potential of GG is lower than that of G, contiguous GG sequences are more readily oxidized by a one-electron oxidant than a single guanine, and OzOz is produced from GG in double-stranded DNA. Unlike most DNA polymerases, DNA polymerase zeta efficiently extends the primer up to full-length across OzOz. (iv) In quadruplex DNA, 3'-guanine is mainly damaged by one-electron oxidation in quadruplex DNA, and this damage depends on the highest occupied molecular orbital (HOMO). The oxidation products in quadruplex DNA are different from those in single-stranded or double-stranded DNA.