WT and E H244A mutant DENV1 prM-E sequences were PCR-amplified from the pGDENV1 3.3 subclones described above, and cloned into pcDNA4/TO (Invitrogen). These constructs were transfected into T-REx TM -293cells using Lipofectamine 2000 (Invitrogen) and selected in T-REx HEK medium containing 125 mg/ml Zeocin, all as previous described [61] .