CHARACTERIZATION AND MOLECULAR-BASIS OF HETEROGENEITY OF THE AFRICAN SWINE FEVER VIRUS ENVELOPE PROTEIN P54

It has been reported that the propagation of African swine fever virus (ASFV) in cell culture generates viral subpopulations differing in pr otein p54 (C. Alcaraz, A. Brun, F. Ruiz-Gonzalvo, and J. M. Escribano, Virus Res. 23:173-182, 1992). A recombinant bacteriophage expressing a 328-bp fragment of the p54 gene was selected in a lambda phage expre ssion library of ASFV genomic fragments by immunoscreening with antibo dies against p54 protein. The sequence of this recombinant phage allow ed the location of the p54 gene in the EcoRI E fragment of the ASFV ge nome. Nucleotide sequence obtained from this fragment revealed an open reading frame encoding a protein of 183 amino acids with a calculated molecular weight of 19,861. This protein contains a transmembrane dom ain and a Gly-Gly-X motif, a recognition sequence for protein processi ng of several ASFV structural proteins. In addition, two direct tandem repetitions were also found within this open reading frame. Further c haracterization of the transcription and gene product revealed that th e p54 gene is translated from a late mRNA and the protein is incorpora ted to the external membrane of the virus particle. A comparison of th e nucleotide sequence of the p54 gene carried by two Virulent ASFV str ains (E70 and E75) with that obtained from virus Ba71V showed 100% sim ilarity. However, when p54 genes from viral clones generated by cell c ulture passage and coding for p54 proteins with different electrophore tic mobility were sequenced, they showed changes in the number of copi es of a 12-nucleotide sequence repeat. These changes produce alteratio ns in the number of copies of the amino acid sequence Pro-Ala-Ala-Ala present in p54, resulting in stepwise modifications in the molecular w eight of the protein. These duplications and deletions of a tandem rep eat sequence array within a protein coding region constitute a novel m echanism of genetic diversification in ASFV.