Mechanism of influenza recombination. I. Factors influencing recombination rates between temperature-sensitive mutants of strain WSN and the classification of mutants into complementation--recombination groups.

Abstract

Mixed infection of chick embryo fibroblasts with ts mutants of WSN virus resulted in a number of reeombinant-yielding cells far in excess of what was predicted in terms of the adsorbed multiplicity of the plaque-forming virus employed. Some pairs of mutants had a strong tendency to form mixed aggregates which gave rise to recombinants by a single hit process. Reeombinant-yielding cells were also generated by a two-hit mechanism, in which case the yield of mixedly infected cells (recombinant yielders) exceeded the expectation (based on the number of plaque-forming particles adsorbed) by a factor of 30–60 times. These results reinforce the previously proposed conclusion that non-plaque-forming particles are the principal source of recombinants in mixed infection. The two-hit recombinant-yielding cells were obtained at exceedingly low virus inputs and were obtained in cells that were incubated solely at the restrictive temperature for the ts mutants employed. This undoubtedly means that the initial steps leading to recombinant production were the result of complementation, followed at maturation by an exchange of RNA pieces which in some cases gave wild-type particles. These results strongly suggest that non-plaque-forming virus has the capacity to enter cells and generate some syntheses such as the formation of messenger RNA and viral structural proteins. They also suggest that two non-plaque-forming particles, each bearing a mutation on a different RNA piece, may by means of complementation and recombination, give rise to wild-type virus. On the basis of complementation-recombination patterns a number of mutant strains have been classified into eight groups. Members of each group give high frequency complementation-recombination with each of the other groups. The physiological basis of the classification is being investigated.