A specific sub-set of host-cell mRNAs prime influenza virus mRNA synthesis.

The host-cell derived RNA primer sequences at the 5' termini of mRNAs of influenza A and B viruses, obtained from sequences of 29 cDNA clones, have been compared. This has been done for clones of five different genome segments from four strains of influenza A and B virus. The results indicate that host RNA primers containing a 3'-terminal Py-G-C-A sequence before the presumed endonuclease cleavage site are preferred for use as primers in influenza virus mRNA synthesis. Primer-extension analyses of the 5'-terminal heterogeneous sequences of in vivo synthesized mRNAs confirm the preference for G-C-A-terminated primer fragments, with some differences noted between the transcripts of types A and B influenza virus genome segments.