Further characterization of the virus-specific RNAs in feline calicivirus infected cells

The virus-specific RNAs in feline calicivirus (FCV) infected cells were examined to determine the number and forms of RNAs that are synthesized during the infection process. Northern blots of poly(A)(+) RNA from 5-h infected cells probed with a cDNA clone derived from the 3' end of the FCV genome (pCV3) revealed four FCV-specific RNAs that were approximately 8.2 (genomic RNA), 4.8, 4.2 and 2.4 kb in length. Northern blots of poly(A)(+) RNA purified from infected cells hourly after infection and probed with pCV3 demonstrated that transcription of all FCV-specific RNAs are detectable at 2 to 3 h post-infection (PI) and that these RNAs reached steady state levels at approximately 4 h PI. The levels of the FCV RNAs then remained relatively constant through 7 h PI, the last time tested, with the exception of the 4.8 and 4.2 kb transcripts which showed a marked increase between 6 and 7 hours PI. Northern blots of dsRNA which had been LiCl-fractionated from pooled total cellular RNA isolated from 5-h and 7-h FCV infected cells, showed two double-stranded RNAs corresponding to the 8.2 kb genomic RNA and the 2.4 kb subgenomic RNA. Preliminary mapping by Northern blotting using cDNA probes derived from varying locations within the FCV genome was done to determine the approximate regions from which the subgenomic RNAs are derived. This analysis indicates that the viral RNAs are nested, co-terminal transcripts with common 3' ends.