Common Sequence at the 5′ Ends of the Segmented RNA Genomes of Influenza A and B Viruses

Abstract
Guanylyl- and methyltransferases, isolated from purified vaccinia virus, were used to specifically label the 5'' ends of the genome RNA of influenza A and B viruses. All 8 segments were labeled with [.alpha.-32P]GTP or S-adenosyl[methyl-3H]methionine to form cap structures of the type m7G(5'')pppNm-, of which unmethylated (p)ppN- represents the original 5'' end. Further analyses indicated that m7G(5'')pppAm, m7G(5'')pppAmpGp and m7G(5'')pppAmpGpUp were released from total and individual labeled RNA segments by digestion with nuclease P1, RNase T1 and RNase A, respectively. Consequently, the 5''-terminal sequences of most or all individual genome RNA of influenza A and B viruses were deduced to be (p)ppApGpUp. The presence of identical sequences at the ends of RNA segments of both types of influenza viruses indicates that they were specifically conserved during evolution.