Abstract
To study the mutagenic effects of site-specific, covalent modifications of biologically active DNA, host cells that are permissive for any type of mutation that might be produced in vivo from the modified DNA are needed. Specifically, a general in vivo complementation system for the bacteriophage .vphi.X174 gene G, an essential gene that was chosen for initial studies of chemical mutagenesis, is required. A plasmid (p.vphi.XG) that carries a functional copy of .vphi.X174 gene G was constructed. Three different bacterial strains that are nonpermissive for am9, a gene G amber mutant, were transformed with p.vphi.XG. The transformants are now permissive for this gene G mutant, but not for the gene A or E mutants that were tested. This paper describes the construction and the biochemical characterization of this plasmid, p.vphi.XG, and describes some of the biological properties exhibited by the p.vphi.XG-bearing strains.