Yellow fever 17D virus: pseudo-revertant suppression of defective virus penetration and spread by mutations in domains II and III of the E protein

Abstract

A yellow fever (YFV) 17D virus variant, which causes persistent infection of mouse neuroblastoma cells associated with defective cell penetration and small plaque size, yielded plaque-revertant viruses from cells transfected with viral transcripts encoding the adaptive mutation (Gly 360 in the E protein). Reconstruction of a plaque-purified revertant which contained Gly 360 and additional substitutions (Asn for Lys 303 and Val for Ala 261) yielded a virus whose infectious center size, growth efficiency, and cell penetration rate similar to the parental YF5.2iv virus, whereas viruses with Asn 303 or Val 261 alone with Gly 360 yielded either a small-plaque virus or a parental revertant. These data indicate that the YFV E protein is subject to suppression of mutations in domain III that are deleterious for viral entry and spread by a second-site mutation in domain II. Position 261 lies within the hydrophobic ligand-binding pocket at the domain I–II interface, a site believed to be involved in the hinge-like conformational change of domain II during activation of membrane fusion-activity. Results of this study provide genetic data consistent with findings on flavivirus structure and implicate domain III in functions beyond simply cell surface attachment.