Interferon induction by transfection of Sendai virus C gene cDNA

To elucidate the mechanism of interferon (IFN) induction on virus infection, we constructed two types of plasmids by inserting a part of the cDNA of the Sendai virus into a simian virus 40-derived expression vector (pSV2-0). One, pSV2-PC, contained the P + C gene, which codes for the P and C proteins in overlapping reading frames, and the other, pSV2-C, contained only the C gene. After transfecting the plasmids into mammalian cells, we determined the IFN activity in the culture medium. We found that the level obtained with pSV2-PC was significantly positive but very low, whereas that obtained with pSV2-C was as high as or even higher than that observed in the culture medium after Sendai virus infection. By cleaving pSV2-C between the simian virus 40 promotor and the C gene or by inserting a stop codon within the C gene [pSV2-C(stop)], induction of IFN was greatly diminished. In Northern blot analyses of the transcripts obtained from the cells transfected with the plasmids with cDNA to the P + C gene as a probe, the transcript having the expected size was detected with both pSV2-C and pSV2-C(stop), whereas none was detected with cleaved pSV2-C or pSV2-0. The results indicate that both transcription and translation of the C gene seem to be required for IFN induction after Sendai virus infection.