A possible partial heterozygote of an influenza a virus

Abstract The gene constellation of recombinants between temperature-sensitive ( ts ) mutants of fowl plaque virus (FPV) and other prototype influenza A strains were analyzed by reciprocal molecular hybridization. Of 40 recombinants tested, only one (19/N) was found which carried RNA segments 3 (polymerase 2 gene) and 6 (neuraminidase gene) of FPV as well as those of virus N. Neuraminidase activity of FPV was fully expressed in cells infected with 19/N, whereas the enzyme activity of virus N was not detected. Virus N neuraminidase, however, was still synthesized as an antigen. During further plaque passages, this isolate finally segregated into stable recombinants carrying segment 3 either from the one or the other parent and segment 6 of FPV. Plaque isolates carrying segment 6 of both parents lost the gene which codes for the virus N neuraminidase in a stepwise manner during further passages through embryonated eggs. Using a specific antiserum against FPV neuraminidase, isolates were obtained which carried only the defective virus N neuraminidase gene. These isolates formed normal sized plaques and induced extremely low enzyme activities, although neuraminidase as an antigen was still produced. The data so far available make it unlikely that the original isolate consisted of a mixture of different recombinants and indicate that it represents an individual partial heterozygote.