Mutation hotspots in the gpt gene in the small intestine of Msh2-bearing mice (+/+) carrying gpt and Msh2-KO mice (−/−) carrying gpt. Potassium bromate (1.5 g/L) (Br) in the drinking water or the vehicle control (C) was administered for 28 days. Numbers in the column next to the groups of animals are animal identification numbers shown in Additional Table S1. The letters A, G, T, and C indicate the bases substituted or inserted; and d and (AA) indicates deletion of base and insertion of two adenine residues, respectively. The number of letters in brackets are the number of clonal mutants. A blue arrow indicates the position of base insertion. Light blue letters are the parts of gpt sequence, and red letters in the gpt sequence, the dashed lines and the number above the sequence indicate the nucleotides of mutation hotspots, the positions of mutation hotspots and the nucleotide number, respectively.