West Nile virus envelope proteins: nucleotide sequence analysis of strains differing in mouse neuroinvasiveness

Nile (WN) viruses were characterized by nucleotide sequencing of their envelope (E) protein regions. Prolonged passage in mosquito cells caused loss of neuroinvasiveness and acquisition of an N-linked glycosylation site, which is utilized. Limited passage in cell culture also caused glycosylation but not attenuation, suggesting that glycosylation may not be directly responsible for attenuation and that a second mutation (L68!P) may also be involved. A monoclonal antibody-neutralization escape mutant with a substitution at residue 307, a site common to other flavivirus escape mutants, was also atten-uated. A partially neuroinvasive revertant regained the parental E sequence, implying that determi-nants outside of the E region may also influenc