RNA polymerase of influenza virus. Dinucleotide-primed initiation of transcription at specific positions on viral RNA.

The priming activities of dinucleotides of all possible base sequences as to the transcription initiation by influenza virus-associated RNA polymerase were investigated. Dinucleotide ApG, complementary to positions 1-2 from the 3' termini of viral RNA segments, was the most active primer and directed the formation of ApGpC; dinucleotide GpC, complementary to positions 2-3, was also an active primer and directed the formation of either GpCpG or GpCpA; but both dinucleotides CpG and CpU, complementary to positions 3-4, were virtually inactive. These results indicate that the transcription is initiated within the first four nucleotides at the 3' termini of viral RNA. Among other dinucleotides, only those hybridizable to viral sequences at their 3'-proximal bases were partially active, implying the essential role of base pairing immediately next to the first phosphodiester bond.