C-->T transition mutations are not solely UVB-signature mutations, because they are also generated by UVA.

In this issue, Ikehata et al. confirm data from cell culture models by showing that the C-->T transition mutation is also the most common UVA-generated mutation in vivo. This indicates that DNA photoproducts are the most important premutagenic lesions not only in UVB mutagenesis, but also in UVA mutagenesis. C-->T transitions cannot therefore be considered solely UVB-signature mutations. In addition, there is no consistent evidence for a separate UVA-generated UVA signature mutation. We hypothesize that weaker anti-mutagenic cellular responses to UVA, as compared to UVB, may result in higher rates of mutation formation for UVA-induced dimers.