Our studies on the REV2-dependent processes of DNA repair and u.v. mutagenesis in yeast are summarized and compared with the general features of DNA damage-induced mutagenesis in yeast. On the basis of the data available, we propose that mismatch repair is an essential process in u.v. mutagenesis. We assume that a photoproduct site in double-stranded DNA can be handled as a replicative mismatch leading to misinsertion opposite the lesion.