Nucleotide sequence and expression of the capsid protein gene of feline calicivirus

Abstract

The sequence of the 3'-terminal 2,486 bases of the feline calicivirus (FCV) genome was determined. This region of the FCV genome, from which the 2.4-kb subgenomic RNA is derived, contained two open reading frames. The larger open reading frame, found in the 5' end of the subgenomic mRNA, contained 2,004 bases encoding a polypeptide of 73,467 Da. The smaller open reading frame, encoded in the 3' end of the mRNA, was composed of 318 bases, encoding a polypeptide of 12,185 Da. The AUG initiation codon of the second open reading frame overlapped the UGA termination codon of the first, with the sequence AUGA. The nucleotide sequence of the region containing this overlap resembles the -1 frameshift sequences of the retroviruses. The 5' end of the 2.4-kb subgenomic RNA was mapped by primer extension analysis. There were two apparent transcription initiation points, both of which were 5' to the AUG initiation codon of the large open reading frame. Transcription from these sites yielded RNA transcripts with 5' nontranslated leader regions of 17 and 18 bases. The total length of the 2.4-kb subgenomic RNA was 2,375 bases (from the 5'-most start site) excluding the poly(A) tail. Edman degradation of the purified capsid protein of FCV showed that the capsid protein was encoded by the large open reading frame. Western immunoblot analysis of FCV-infected cells using a feline anti-FCV antiserum demonstrated that translation of the capsid protein was detectable at 3 h postinfection and continued to accumulate until 8 h postinfection, the last time examined.