HETEROLOGOUS RECOMBINATION IN THE SEGMENTED DSRNA GENOME OF BACTERIOPHAGE-PHI-6

The genome of bacteriophage Phi 6 is composed of three unique segments of double-stranded RNA packaged within a procapsid. One segment can r ecombine with another in regions that share little sequence similarity . Although the recombination is therefore heterologous, the crossover points usually consist of two to six identical nucleotides. The freque ncy of recombinants is enhanced by conditions that prevent or hinder t he minus strand synthesis of a single plus strand segment. Recombinati on serves as a repair system as well as a means of changing the geneti c structure of the virus. The reaction can be studied in an in-vitro p ackaging and replication system involving purified procapsids and ssRN A. Although there are striking differences in the mechanisms of recomb ination in RNA viruses, there are also strong similarities. All seem t o use a copy-choice template switching action for recombination. The P hi 6 system is a useful model for the recombination of other segmented double-stranded RNA viruses such as the Reoviridae.