Synthesis of subgenomic mRNA's of mouse hepatitis virus is initiated independently: evidence from UV transcription mapping.

The target sizes of the templates for the synthesis of the genome-sized RNA and the six subgenomic RNAs found in cells infected with mouse hepatitis virus strain A59 were determined by UV transcription mapping. Infected Sac(-) cells were irradiated at 6 h postinfection, the time when virus-specific RNA synthesis starts to increase exponentially. The effect of increasing UV doses on the synthesis of the individual RNAs was determined by quantitation of these RNAs after separation by agarose gel electrophoresis. The UV target sizes calculated for the templates were almost identical to the physical sizes of the RNAs. The results of these experiments seem to exclude the possibility that the subgenomic RNAs are processed or spliced from a common precursor. The data are consistent with independent initiation of transcription on a genome-sized, negative-stranded template or on smaller templates.