A conserved African swine fever virus right variable region gene, I1 1L, is non-essential for growth in vitro and virulence in domestic swine

The right variable region of the African swine fever virus (ASFV) genome is known to contain genes with functions involving virus virulence and host range in swine. A novel open reading frame, ORF I1 1L, which was absent in the non-pathogenic, cell culture-adapted European isolate BA71V, was identified in the pathogenic African isolate Malawi Lil-20/1. The location of I1 1L in the right variable region, together with its absence in BA71V, suggested that I1 1L may have a function in virus virulence and/or host range. Here, we show that the I1 1L gene is highly conserved among pathogenic African, European and Caribbean ASFV field isolates and that it exists either in a short form, encoding a protein of 77-78 amino acids (9.1 kDa) or in a longer form of 93-94 amino acids (11.1 kDa). The presence of two predicted membrane-spanning segments suggests that I1 1L is an integral membrane protein. RT-PCR analysis demonstrated that I1 1L mRNA is expressed late in the virus replication cycle. A recombinant I1 1L gene deletion mutant, ΔI1 1L, was constructed from the ASFV isolate Malawi Lil-20/1 to examine gene function. Deletion of I1 1L did not affect virus replication in swine macrophage cell cultures nor virulence in domestic pigs, indicating that I1 1L is non-essential for growth in vitro and for virus virulence in domestic swine.