Activation of influenza virus-associated RNA polymerase by cap-1 structure (m7GpppNm).

During the generation of primer for transcription initiation by endonucleolytic cleavage of capped RNA, the influenza virus-associated RNA-dependent RNA polymerase recognizes three signals of capped RNA, i.e., cap-1 structure at 5' termini, RNA sequences at the cleavage sites, and distance between these two signals (Plotch, S.J., Bouloy, M., & Krug, R.M. (1979) Proc. Natl. Acad. Sci. U.S. 76, 1618-1622; Kawakami, K., Mizumoto, K., & Ishihama, A. (1983) Nucl. Acids Res. 11, 3637-3649). The free cap-1 structure, i.e., m7GpppNm not associated with polynucleotides, stimulates the RNA synthesis as well, irrespective of the presence or absence of dinucleotide primers. Since the stimulation by m7GpppNm and ApG is additive and the free cap-1 structure is not incorporated into 5' termini of product RNA, we propose that the cap-1 structure stimulates the RNA polymerase by allosteric modulation rather than by priming the transcription initiation.