Sequence analysis of the membrane protein V3 of the flavivirus West Nile virus and of its gene.

Flaviviruses contain a large membrane-associated protein V3, having a mol mass of about 50 kDa which is responsible for hemagglutination. We have isolated the V3 protein from the West Nile (WN) flavivirus and determined its amino-terminal amino acid sequence and amino acid sequences of fragments derived from this protein. We have also transcribed parts of the WN virus genome RNA into cDNA and cloned and sequenced this cDNA. The results of these analyses have allowed us to identify the region of the viral genome coding for the V3 protein. In this report we describe the total nucleotide sequence of the genome region coding for the WN virus V3 protein and the amino acid sequence of the V3 protein derived from these analyses. The exact carboxy terminus of the V3 protein has not been determined in these experiments. These analyses have shown that the V3 protein of WN virus does not contain an Asn-X-Ser/Thr sequence which could allow addition of N-linked carbohydrate chains to this protein. In accordance with this finding, analyses of metabolic labeling of the V3 protein using [3H]glucosamine indicate that the WN virus V3 protein is an unglycosylated protein. Together with our earlier analyses these results show that the viral structural proteins are present on the genome RNA in the order 5'-terminus-core protein (V2)-small membrane-associated protein (NV2)-large membrane-associated protein (V3) and describe the nucleotide sequences coding for all WN virus structural proteins identified so far. A hypothesis concerning the processes involved in the synthesis of all viral structural proteins and the probable orientation of these proteins relative to the endoplasmatic reticulum membrane based on the structure of these proteins is discussed.