Virus and host cell-dependent variation in transcription of the mumps virus genome.

Evidence has been presented that generation of polycistronic readthrough RNAs in mumps virus-infected cells is not a simple stochastic process with strain-dependent variations in the generation of certain readthrough products, but that this process is affected by host as well as viral factors. RNAs extracted from infected Vero cells or chicken embryo fibroblast (CEF) cells have been analysed by Northern blotting with virus-specific probes for the nucleocapsid (N), phosphoprotein (P), matrix (M), fusion (F), small hydrophobic (SH) and haemagglutinin-neuraminidase (HN) genes. Vero cells infected with tissue culture cell-adapted virus strains generate monocistronic as well as polycistronic RNAs. Transcription analysis of Vero cells infected with an egg-adapted strain reveal the absence of monocistronic M and F transcripts, with a concomitant increase in readthrough transcripts involving these genes. When the same virus infects CEF cells monocistronic RNAs accumulate. The presence of viral proteins in the various virus/host cell combinations assessed by immunofluorescence with mumps virus-specific monoclonal antibodies for the N, P, M, F and HN proteins correlates well with the patterns of transcription.