An improved system for selection of forward mutations in an Escherichia coli supF gene carried by plasmids

An improved system to examine forward mutations that occurred in the supF g ene of Escherichia coli carried on a multicopy plasmid is described. The sy stem was validated by measuring spontaneous mutations of supF plasmids prop agated in wild-type, recA(-) and mutM(-) mutY(-) E. coli strains, the mutat ion frequencies of which were 1.3 x 10(-7), 6.3 x 10(-7) and 1.5 x 10(-6), respectively. Sequence analysis of the supF mutant plasmids revealed that G :C-->T:A and G:C-->C:G transversions dominated. This improved system allows rapid scoring and sequencing forward mutations in the supF gene, thus perm itting its use as a genetic target for repair and mutagenesis studies in ba cteria and mammalian cells.