For radioactive immunoprecipitation, DENV2-infected BHK-21 cells were harvested 48 hr later and prepared as described previously [18] . For immunoprecipitation with SDS to disrupt protein complexes, lysate from infected cells was incubated with 1.25% SDS for 30 min at 4 o C. The SDS concentration was diluted to 0.2% before immunoprecipitation and precipitated proteins were analysed by silver stained SDS-PAGE (Silver stain Plus Kit, Bio-Rad) and Western blot.