A BIR Motif Containing Gene of African Swine Fever Virus,4CL,Is Nonessential for Growthin Vitroand Viral Virulence

Abstract

An African swine fever virus (ASFV) gene with similarity to viral and cellular inhibitor of apoptosis genes (iap) has been described in the African isolate Malawi Lil-20/1 (ORF 4CL) and a cell-culture-adapted European virus, BA71V (ORF A224L). The similarity of the ASFV gene to genes involved in inhibiting cellular apoptosis suggested the gene may regulate apoptosis in ASFV-infected cells and thus may function in ASFV virulence and/or host range. Sequence analysis of additional African and European pathogenic isolates demonstrates that this gene is highly conserved among both pig and tick ASFV isolates and that its similarity toiapgenes is limited to the presence of a single IAP repeat motif (BIR motif) in the ASFV gene. To study gene function, a4CLgene deletion mutant, Δ4CL, was constructed from the pathogenic Malawi Lil-20/1 isolate. Growth characteristics of Δ4CL in swine macrophage cell cultures were indistinguishable from those of parental virus. Infected macrophage survival time and the induction and magnitude of apoptosis in virus-infected macrophages were comparable for cells infected with either Δ4CL or parental virus. In infected swine, Δ4CL exhibited an unaltered Malawi Lil-20/1 virulence phenotype. These data indicate that, although highly conserved among ASFV isolates, the4CLgene is nonessential for growth in macrophage cell culturesin vitroand for pig virulence. Additionally, despite its limited similarity toiapgenes,4CLexhibits no anti-apoptotic function in infected macrophage cell cultures. The high degree of gene conservation among ASFV isolates, together with the apparent lack of function in the swine host, suggests4CLmay be a host range gene involved in aspects of infection in the arthropod host, ticks of the genusOrnithodoros.