Positive identification of NS4A, the last of the hypothetical nonstructural proteins of flaviviruses.

A radiolabeled protein migrating in SDS-polyacrylamide gels near the core protein C of Kunjin virus-infected cells was isolated and subjected to N-terminal amino acid sequencing. Comparisons with the translation sequence deduced from the known nucleotide sequence identified a hydrophobic protein of 149 amino acids located in the polyprotein sequence between NS3 and NS4B, thus establishing its identity as NS4A with a calculated Mr 16,100. The cleavage sites identified at the N- and C-termini are KR decreases S....parallel....VAA decreases, both representing consensus sequences defined previously for Kunjin and other flaviviruses.