Sendai virus gene expression in lytically and persistently infected cells

Sendai virus RNA species were quantitated in lytically and persistently infected cultured cells by Northern blot hybridization to region- and strand-specific cloned cDNA probes. Levels of NP, P and M mRNA in lytically infected cells were equally high, but F and HN mRNA were present in about 3-fold, and L mRNA in 30-fold, lower amounts, reflecting transcriptional attenuation especially at the M-F and HN-L gene junction. Two persistently infected cell lines, which release only 1% of the virus particles of lytically infected cells, were shown to contain only 4- to 8-fold-less amounts of each viral mRNA and 2- to 3-fold-less genomic RNA than lytically infected cells. Additionally, transcription was neither defective nor more attenuated as compared to the lytical infection. Taken together the results suggest the existence of an additional regulatory mechanism for the virus release. A cell-associated state of infection therefore seems to be achievable by a relatively weak general reduction of the copy numbers of viral mRNA and genomic RNA.