THE CLONING, SEQUENCING AND EXPRESSION OF A MAJOR ANTIGENIC REGION FROM THE FELINE CALICIVIRUS CAPSID PROTEIN

RNA purified from the feline calicivirus (FCV) F9 vaccine strain was used to prepare a cDNA library in the expression vector lambda-gt11. The library was screened for expression of FCV antigen using a rabbit antiserum prepared against purified FCV. A 330 bp cDNA clone was identified and used as a probe to obtain a larger overlapping clone of 1369 bp. Comparative sequence analysis with the CFI and F4 strains showed that the clones were derived from the 3' open reading frame encoding the capsid protein. The region encoded by the 330 bp clone was shown to be variable in the three strains compared, and therefore the probable location of major antigenic variation. This clone was expressed in a bacterial system and antiserum to the recombinant protein was used in immunoblots to confirm that this clone was derived from the gene encoding the capsid protein. From these immunoblots, several other capsid-related polypeptides were identified. Comparison with immunoblots using post-vaccination cat sera showed the antibody response in the cat was directed mainly against the capsid protein. Antiserum to the recombinant protein was shown to be effective in neutralizing the infectivity of FCV, indicating that at least one major neutralizing epitope had been cloned.