Spectrum of spontaneous mutation at the APRT locus of Chinese hamster ovary cells: An analysis at the DNA sequence level

Abstract

The spectrum of spontaneous mutation of an endogenous mammalian cell gene has been determined at the DNA sequence level. Thirty independent spontaneous APRT- mutations were cloned and subsequently completely sequenced. Twenty-seven contained single base substitutions. Of these, 22 were G·C to A·T transitions, suggesting a major role for the deanimation of cytosine in spontaneous mutagenesis of Chinese hamster ovary cells. The remaining mutants included a tandem double substitution, a -1-frameshift, and a 17-base-pair deletion flanked by a 2-base-pair direct repeat. Many of the independently recovered mutants were clustered at sites of multiple occurrence (hot spots). One site accounted for >25% of all independently recovered events. Mutations were generally located within the coding sequence, although two mutations occurred within the consensus sequence for a 3' splice site.