Expression of Sendai virus defective-interfering genomes with internal deletions

Sendai virus strain 7 has been shown to contain four defective interfering (DI) RNA species in which both genome termini and various adjacent fragments of the 3'-terminal NP gene and 5'-terminal L gene are represented, but most or all internal genes and gene boundaries are deleted. Previous sequence analyses of these mutant RNAs suggested that all four possessed the transcription initiation signal of the NP gene and the transcription termination signal of the L gene. The supposition that these signals should specify transcripts has now been supported by oligo(dT) selection of four DI 7 specific RNA species that had apparent molecular weights slightly lower than each DI genome. DI RNA 7a, which contains the entire NP gene, except for two U residues at the end of the poly(A) initiation signal, appeared to be transcribed solely as a readthrough product. Since DI RNA 7a contains the entire NP protein-coding sequence and DI RNAs 7c and 7d contain fragments of it, whereas DI RNA 7b is devoid of it, only transcripts of RNAs 7c and 7d were expected to specify fusion proteins containing NP gene-specific sequences. A strain 7-induced protein that reacted with monoclonal antibodies against the NP protein had the 33,000 Mr size appropriate for the translation product predicted by the sequence of RNA 7d. Other proteins of lower molecular weight were seen only in cells infected by strain 7, but they did not react with NP-specific antibody and their translation in vitro was not blocked by hybridization to an NP gene-specific oligonucleotide. Therefore, at least some of these proteins may be cellular products induced by DI virus infection. These DI transcripts and translation products may influence interference with replication of the parental helper virus.