Abstract
In order to study mutagenesis in mammalian cells, stable mouse L-cell lines were established with multiple copies of a lambda phage vector that contains the supF gene of Escherichia coli as a target for mutagenesis. Rescue of viable phage from high molecular weight mouse cell DNA using lambda in vitro packaging extracts was efficient (5 phage per microgram of cell DNA per copy) and yielded a negligible background of mutant phage (0 out of 54,605). From mouse cells exposed to 254-nm ultraviolet light (12J/m2), 78,510 phage were rescued, of which 8 were found to have mutant supF genes. DNA sequence analysis of the mutants suggests that the primary site of UV mutagenesis in mammalian cells is at pyrimidine-cytosine (Y-C) sequences, and that the most frequent mutation at this site is a C----T transition.