Figure 3.

8-oxoguanine formation and cytosine deamination are highly dominating on the transcribed strand in isolated papillae. (a) Assuming that all identified G-T and C-A transversions are the result of 8-oxoguanine formation, and all G-C to A-T transitions are the result of cytosine deamination, we analysed the localisation of the corresponding G- and C- residues in the 96 sequenced mutant genomes and in (b) the 594 sequenced crp sequences. Only missense mutations were analysed. (c) Upper panel: Illustration of the mechanism of retromutagenesis after 8-oxoguanine (encircled G) formation on the transcribed strand (ts, dark grey line) that enables insertion of an adenine ribonucleotide in the mRNA (green waved line). The mutated mRNA enables growth and a round of replication that permanently fixes the mutation on the coding strand (cs, light blue line) in daughter cells. Lower panel: 8-oxoguanine formation on the coding strand does not transfer to daughter cells. (d) Illustration of retromutagenesis after cytosine nucleotide deamination into uracil (encircled U), enabling base pairing with A. Upper and lower panels show result of cytosine deamination on transcribed and coding strand respectively, as detailed in (c).