THE 3 SUBUNITS OF THE POLYMERASE AND THE NUCLEOPROTEIN OF INFLUENZA-BVIRUS ARE THE MINIMUM SET OF VIRAL-PROTEINS REQUIRED FOR EXPRESSION OF A MODEL RNA TEMPLATE

The genes encoding the nucleoprotein, PB1, PB2, and PA proteins of the influenza virus strain B/Panama/45/90 have been cloned under control of the T7 RNA polymerase promoter of plasmid pGEM-3. Transfection of t he recombinant plasmids obtained into mammalian cells, which had been infected with a vaccinia virus encoding the T7 RNA polymerase, resulte d in expression of the expected influenza B virus polypeptides. Moreov er, it is shown that coexpression of the four recombinant core protein s in COS-1 cells reconstituted a functional polymerase capable of expr essing a synthetic influenza B virus-like CAT RNA. By using the influe nza B virus recombinant plasmids and a set of pGEM-derived plasmids en coding the homologous core proteins of the influenza A virus A/Victori a/3/75 (I. Mena et al. (1994). J. Gen. Virol. 75, 2109-2114), the capa bilities of home-and heterotypic mixtures of the four core proteins to express synthetic type A and B CAT RNAs were analyzed. Both the influ enza A and B virus polymerases were active in expressing, albeit with reduced efficiencies, the heterotypic model CAT RNAs. However, none of all possible heterotypic mixtures of the core proteins reconstituted a functional polymerase. In order to fully characterize the recombinan t plasmids obtained, the nucleotide sequences of the cloned genes were determined and compared to sequences of other type B virus isolates. The results obtained from these latter analyses are discussed in terms of the conservation and evolution of the influenza B virus core genes . (C) 1997 Academic Press.