A BIR MOTIF CONTAINING GENE OF AFRICAN SWINE FEVER VIRUS, 4CL, IS NONESSENTIAL FOR GROWTH IN-VITRO AND VIRAL VIRULENCE

An African swine fever virus (ASFV) gene with similarity to viral and cellular inhibitor of apoptosis genes (lap) has been described in the African isolate Malawi Lil-20/1 (ORF 4CL) and a cell-culture-adapted E uropean virus, BA71V (ORF A224L). The similarity of the ASFV gene to g enes involved in inhibiting cellular apoptosis suggested the gene may regulate apoptosis in ASFV-infected cells and thus may function in ASF V virulence and/or host range. Sequence analysis of additional African and European pathogenic isolates demonstrates that this gene is highl y conserved among both pig and tick ASN isolates and that its similari ty to lap genes is limited to the presence of a single IAP repeat moti f (BIR motif) in the ASFV gene. To study gene function, a 4CL gene del etion mutant, Delta 4CL, was constructed from the pathogenic Malawi Li l-20/1 isolate. Growth characteristics of Delta 4CL in swine macrophag e cell cultures were indistinguishable from those of parental virus. i nfected macrophage survival time and the induction and magnitude of ap optosis in virus-infected macrophages were comparable for cells infect ed with either Delta 4CL or parental virus. in infected swine, Delta 4 CL exhibited an unaltered Malawi LiI-20/1 Virulence phenotype. These d ata indicate that, although highly conserved among ASN isolates, the 4 CL gene is nonessential for growth in macrophage cell cultures in vitr o and for pig virulence. Additionally, despite its limited similarity to lap genes, 4CL exhibits no anti-apoptotic function in infected macr ophage cell cultures. The high degree of gene conservation among ASN i solates, together with the apparent lack of function in the swine host , suggests 4CL may be a host range gene involved in aspects of infecti on in the arthropod host, ticks of the genus Omithodoros. (C) 1997 Aca demic Press.