DNA sequence analysis of conserved and unique regions of swinepox virus: identification of genetic elements supporting phenotypic observations including a novel G protein-coupled receptor homologue.

Swinepox virus (SPV) contains a double-stranded cross-linked linear DNA genome of approximately 175 kilobase pairs with terminal inverted repetitions (TIRs) of 4.3 kb. The nucleotide sequence was determined for fragments from several regions of the genome including a 2.85-kb fragment from the central potentially conserved portion and two fragments within the presumed variable near-terminal regions which tend to be unique to a given poxvirus. The core sequence contains one partial and two complete open reading frames that are highly conserved and colinear with three contiguous ORFs within the HindIII D fragment of vaccinia virus (VV). The two near-terminal fragments, encompassing 14.2 and 3.6 kb, are respectively located 2.1 kb internal to the left and right cross-linked termini of the DNA and span the TIR junctions. The sequences encode 25 open reading frames including numerous proteins predicted to be membrane-bound or secreted in infected cells. Several ORFs unique to SPV were identified that may be involved in cell attachment, immune modulation, and pathogenesis including a novel poxvirus G protein-coupled receptor. In addition, several polypeptides encoded within the near-terminal regions of vaccinia virus DNA that function as host range or virulence factors are lacking within this region of swinepox virus including the VV growth factor, complement-binding protein, and ORFs C7L and K1L, associated with host range. The lack of these functional homologues could explain the characteristic attenuated phenotype and limited host range of SPV.