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Abstract

RNA polymerase I transcription in vivo in transiently DNA-transfected cells has been used for expression of influenza vRNA molecules coding for chloramphenicol acetyltransferase (CAT) in anti-sense orientation. Influenza virus superinfection served to provide viral RNA polymerase and other proteins for transcriptional conversion of minus-strand vRNA into plus-strand viral mRNA molecules expressing CAT activity. This system has been used for an analysis via nucleotide exchanges as well as deletions and insertions of both terminal segments of the vRNA sequence which cooperatively constitute the vRNA promoter structure. Several mutants with greatly enhanced expression rates over wild-type levels have been constructed, which also can be packaged and serially passaged into progeny virus. The data obtained for the mutations in various promoter elements support a model of consecutive, double strand vRNA promoter structures in binding of viral polymerase and initiation of RNA synthesis. Preparations of attenuated influenza virus for vaccination purposes include a single recombinant segment with promoter up mutation(s) for over-expression of an own or foreign gene product, which at the same time because of its over-replication serves to decrease the number of helper virus RNP segments. The same viruses further have been passaged through a step of ribozyme cleavage acting at one of the helper viral segments, which will delete this vital function and structure with high rates from the virus progeny. The resulting attenuated viruses will interact with their target cells in only one round of abortive infection, and are unable to produce viral progeny.

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First Claim