Molecular characterization of guinea pig-adapted variants of Ebola virus

Serial passage of initially nonlethal Ebola virus (EBOV) in outbred guinea pigs resulted in the selection of variants with high pathogenicity. Nucleot ide sequence analysis of the complete genome of the guinea pig-adapted vari ant 8mc revealed that it differed from wild-type virus by eight mutations. No mutations were identified in nontranscribed regions, including leader, t railer, and intragenic sequences. Among noncoding regions the only base cha nge was found in the VP30 gene. Two silent base changes were found in the o pen reading frame (ORF) encoding NP protein. Nucleotide changes resulting i n single-amino-acid exchanges were identified in both NP and L genes. Three other mutations found in VP24 caused amino acid substitutions, which are r esponsible for larger structural changes of this protein, as indicated by a n alteration in electrophoretic mobility. A highly pathogenic EBOV variant K5 from another passaging series showed an amino acid substitution at nearl y the same location in the VP24 gene, suggesting the importance of this pro tein in the adaptation process. In addition, sequence variability of the GP gene was found when plaque-purified clones of EBOV-8mc were analyzed. Thre e of five viral clones showed insertion of one uridine residue at the GP ge ne-editing site, which led to a significant change in the expression of vir us glycoproteins. This observation suggests that the editing site is a hot spot for insertion and deletion of nucleotides. not only at the level of tr anscription but also of genome replication. Irrespective of the number of u ridine residues at the editing site, all plaque-purified clones of EBOV var iant 8mc resembled each other in their pathogenicity for guinea pigs, indic ating either the absence or only supportive role of mutations in the GP gen e on the adaptation process, (C) 2000 Academic Press.