FOWLPOX VIRUS ENCODES NONESSENTIAL HOMOLOGS OF CELLULAR ALPHA-SNAP, PC-1, AND AN ORPHAN HUMAN HOMOLOG OF A SECRETED NEMATODE PROTEIN

The genome of fowlpox virus (FWPV), type species of the Avipoxviridae, is considerably rearranged compared with that of vaccinia virus (the prototypic poxvirus and type species of the Orthopoxviridae) and is 30 % larger, It is likely that the genome of FWPV contains genes in addit ion to those found in vaccinia virus, probably involved with its repli cation and survival in the chicken. A 7,470-bp segment of the FWPV gen ome has five open reading frames (ORFs), two of which encode ankyrin r epeat proteins, many examples of which have been found in poxviruses. The remaining ORFs encode homologs of cellular genes not reported in a ny other virus. ORF-2 encodes a homolog of the yeast Sec17p and mammal ian SNAP proteins, crucial to vesicular transport in the exocytic path way, ORF-3 encodes a homolog of an orphan human protein, R31240_2, enc oded on 19p13.2, ORF-3 is also homologous to three proteins (YLS2, YMV 6, and C07B5.5) from the free-living nematode Caenorhabditis elegans a nd to a 43-kDa antigen from the parasitic nematode Trichinella spirali s, ORF-5 encodes a homolog of the mammalian plasma cell antigen PC-1, a type II glycoprotein with exophosphodiesterase activity. The ORFs ar e present in the virulent precursor, HP1, of the sequenced attenuated virus (FP9) and are conserved in other strains of FWPV. They were show n, by deletion mutagenesis, to be nonessential to virus replication in tissue culture. RNA encoding the viral homolog of PC-1 is expressed s trongly early and late in infection, but RNAs encoding the homologs of SNAP and R31240_2 are expressed weakly and late.