Genes encoding fowlpox virus (FWPV) structural
proteins have been identified mainly by sequence homology with those from vaccinia virus (VACV), but little is known about the encoded
proteins. Production of
monoclonal antibodies (MAbs) against Poxine and HP1-440 (Munich) clone FP9 allowed the identification of three immunodominant FWPV
proteins: the 39-kDa core
protein (encoded by FPV168, homologous to VACV A4L), a 30- and 35-kDa
protein doublet, and an abundant 63-kDa
protein. The 30- and 35-kDa
proteins are nonglycosylated, antigenically related
proteins present in the intracellular mature virus membrane and localizing closely with the viral factories. N-terminal sequencing identified the 35-kDa
protein as encoded by FPV140 (the FWPV homolog of VACV H3L). The 63-kDa
protein forms covalently linked dimers and oligomers. It remained mainly insoluble upon
detergent treatment of purified virus but did not localize closely with the viral factory. N-terminal sequencing was unsuccessful, suggesting N-terminal blocking. CNBr digestion generated a
peptide encoded by FPV191, predicted to encode one of two FWPV A-type inclusion (ATI)
proteins. The characteristics of the 63-kDa
protein were inconsistent with published observations on
cowpox or VACV ATI
proteins (it appears to be essential). The 63-kDa
protein, however, shares characteristics with both VACV p4c virus occlusion and 14-kDa fusion
proteins. Gene assignment at the poxvirus ATI locus (between VACV A24R and A28L) is complicated by sequence redundancies and variations, often due to deletions and multiple frameshift mutations. The identity of FPV191 in relation to genes at this locus is discussed.