Effect of preM signal sequence on the secretion of E protein from transfected S2 cells. Cell lysate or culture supernatant was resolved by 12% SDS-PAGE under non-reducing conditions. After electrophoresis proteins were transferred onto nitrocellulose membrane and probed with the antibody 2F2. ECL reagents were used to visualise protein bands. Lanes 1 to 4 are S2/ZF-ZR cell lysate, S2/ZF-ZR culture medium, S2/JEF-JER culture medium and S2/JEF-JER cell lysate respectively.