Interferon induction by viruses. III. Vesicular stomatitis virus: interferon-inducing particle activity requires partial transcription of gene N.

We have measured the interferon-inducing particle (i.f.p.) activity of a ts mutant, GII (I), of vesicular stomatitis virus (VSV) and a non-ts revertant, RI (T1026) in "aged" chick embryo cells and mouse (L(Y) cells at 40.5 and 37.5 degrees C, respectively. Our results suggest that a single i.f.p. suffices to induce a quantum yield of interferon and that there are several times more i.f.p. than plaque-forming particles (p.f.p.) in stock preparations of VSV. Furthermore, while virus replication or amplified RNA synthesis is not required for a particle of VSV to induce interferon, there is a requirement for primary transcription. About one-tenth of the genome must remain intact and be transcribed to synthesize an interferon-inducer moiety. (This represents transcription of about two-thirds of the N protein gene.) We conclude that VSV does not contain a pre-formed inducer of interferon and propose a model for its formation. We suggest that there is a cumulative loss of N (and/or NS and L) protein from the ribonucleoprotein complex during primary transcription, leading ultimately to extensive base-pairing between the genome RNA and its complementary transcript. We suggest that the dsRNA thus formed constitutes the interferon inducer moiety of VSV.