Extragenic suppression of a ts phenotype during recombination between ts mutants of two fowl plague virus strains with a ts mutation in gene 1.

Fowl plague virus (FPV) ts mutants belonging to six recombination groups and obtained from the Weybridge strain (in the U.S.S.R.) or the Rostock strain (in the U.K.) have been studied in a recombination test. Temperature-sensitive mutants obtained from different FPV strains were revealed which had a ts mutation in gene 1; however, their crossing resulted in ts+ recombinants which appeared with a high frequency. This phenomenon was due not to intragenic complementation but to extragenic suppression, when the expression of a ts phenotype of the Rostock strain mutant gene 1 is suppressed by gene 2 products of the Weybridge strain.