Multiple Length Rings of ϕX174 and S13 Replicative Forms

Two temperature-sensitive mutants of the bacterial virus S13 were used to infect Escherichia coli C mixedly in the presence of chloramphenicol. The double stranded circular DNA that constitutes the replicative form of this virus was purified and resolved into its component fractions. The fraction consisting of double length rings was used to infect spheroplasts. Assay of the spheroplast lysates revealed that 0.45% of the liberated phage was wild type. In contrast, when spheroplasts were infected with single length rings only 0.03% of the liberated phage was wild type. These results support the proposal that double length rings are intermediates in genetic recombination.