Priming and Inhibitory Activities of RNAs for the Influenza Viral Transcriptase Do not Require Base Pairing with the Virion Template RNA

Capped ribopolymers lacking a sequence complementary to the common 3′ end of the influenza virion RNA segments effectively stimulated transcription of these RNAs by the virion-associated transcriptase. Thus, stimulation of transcription results not from hydrogen bonding between the capped RNA and the 3′ end of the virion RNA but presumably from a specific interaction of the capped RNA with protein(s) in the transcriptase complex. Although no specific nucleotide sequence was required for priming activity, capped mRNAs with diminished secondary structure were preferred as primers. Inosine-substituted or bisulfite-modified capped reovirus mRNAs were at least 3-to 5-fold more effective as primers than were the native capped mRNAs. On the other hand, inosine substitution or bisulfite treatment of the uncapped form of reovirus mRNAs converted them from essentially inactive species to potent inhibitors of the transcriptase reaction primed by either ApG or globin mRNA. These effects of reduced secondary structure also most probably reflect an interaction of the exogenous RNAs with transcriptase protein(s). The results obtained from screening a series of native uncapped ribopolymers were consistent with inhibitory activity requiring the absence of most hydrogen bonding in the ribopolymer and also suggested that specific structural feature(s) of the nucleotides in the chain were important.