Shuttle vectors carrying the supF suppressor tRNA gene were originally developed for mutagenesis experiments in primate and human cells. Since then, the supF gene has been used as a mutation reporter in other mammalian cells, yeast, Escherichia coli, and transgenic mice. The widespread use of the vector for studies of many DNA reactive agents has produced a large database of mutation spectra. These provide primary information on the kinds and distribution of mutations provoked by many agents and, in many instances, allow comparisons between related agents or the same agent in different cell backgrounds. In this review we will discuss some of these data with a primary focus on the interpretation of UV mutation spectra. We will also describe our development and application of custom supF marker genes as an approach to studying the effect of sequence context on mutation hotspots and cold spots. Our studies suggest that C-C photoproducts are not mutagenic in certain sequence contexts in which T-C photoproducts are mutation hotspots. In addition, we have found several examples of sequence context effects acting as much as 80 bases away from the site of mutation. We will consider some of the problems raised by these studies and the possible resolution of some of them offered by the newly discovered family of damage bypass DNA polymerases.