Sequence analysis of the 3′ end of the feline coronavirus FIPV 79-1146 genome: Comparison with the genome of porcine coronavirus TGEV reveals large insertions

The genetic information, carried on mRNA 6 of feline infectious peritonitis virus (FIPV) strain 79–1146, was determined by sequence analysis of cDNA clones derived from the 3′ end of the FIPV genome. Two ORFs were found, encoding polypeptides of 11 K (ORF-1) and 22K (ORF-2). The FIPV sequence was compared to the 3′ end sequence of transmissible gastroenteritis virus (TGEV). ORF-1 has a homologous counterpart (ORF-X3) in the TGEV genome; both ORFs are located at the same position relative to the nucleocapsid gene. However, as a result of an in-frame insertion or deletion, ORF-1 is 69 nucleotides larger than ORF-X3. A similar event has occurred immediately downstream of ORF1: a 624-nucleotide segment, containing the complete ORF-2, is absent in the TGEV sequence. Most sequence similarity (98.5%) was found in the 3′ noncoding sequences. ORF-X3 and ORF-1 are preceded by the sequence AAC-TAAAC, which is assumed to be the transcription-initiation signal in FIPV and TGEV (P. A. Kapke and D. A. Brian (1986)Virology 151, 41–49). By S1 nuclease analysis, the 5′ end of FIPV RNA 6 was mapped immediately upstream of this sequence. A 700-nucleotide TGEV-specific RNA was found by cross-hybridization with an FIPV 3′ end probe, suggesting that TGEV ORF-X3 is also carried on a separate mRNA. The differences at the 3′ ends of the FIPV and TGEV genomes maybe the result of RNA recombination events.