A DNA substitution in the group A streptococcal bacteriophage SP24.

When the group A streptococcal bacteriophage SP24 was propagated on an unrelated host strain CS112, it underwent a DNA rearrangement: the rearrangement involved a substitution of unique DNA (2.5 kb) from an unrelated endogenous prophage carried by strain CS112. This substitution event occurred reproducibly upon infection of strain CS112, as DNAs from a number of independent isolates were found to contain similar, but not identical, DNA sequences. Restriction endonuclease mapping suggested that recombination between homologous sequences shared by the infecting phage and the prophage produced the rearrangement. The recombinant phage was shown to adsorb more rapidly to CS112 cells than did wild type SP24 phage particles: It therefore has a selective advantage during multiple rounds of infection.