Recombination between mutant cauliflower mosaic virus DNAs.

A class of mutants of cauliflower mosaic virus (CaMV) DNA was distinguished based on its members' ability to induce symptoms when coinoculated on plants with other CaMV DNAs mutant at a different locus. Three mutants, one each in open reading frame I, III, and VI had this ability. A second class of mutant DNAs did not induce symptoms unless combined with a mutant DNA of the first class. Viral DNA extracted from diseased plants was shown by restriction enzyme digestion to have lost the mutant alleles. When turnip plants were inoculated with a recombining mutant derived from DNA of the Cabbage S isolate and a mutant derived from DNA of a different isolate, a heterogeneity in the viral DNA extracted from the diseased plants was detected by restriction enzyme analysis. Restriction analysis of cloned representatives of this heterogeneous population revealed regions consistent with repair of heteroduplexes formed during general recombination between duplex DNAs. Some regions consistent with this mechanism or with recombination by strandswitching during reverse transcription were found.