Induction of syncytial formation by baculovirus-expressed flavivirus E proteins. (A) Construction of recombinant baculoviruses. (a) Schematic representation of the flavivirus polyprotein; (b) Structure of recombinant bacmids expressing prME, E, and ectodomain of E (EΔTM) of specific virus. The fragments were inserted into AcMNPV bacmid under the control of a polyhedrin promoter. In the schematic diagram of domain organization for flavivirus E protein, domain I (red), domain II (yellow), and domain III (blue). A stem region links the stably folded E ectodomain with the C-terminal transmembrane anchor. (B) Morphology of Sf9 cells at 120 h after transfection with Ac-ZprME, Ac-ZE, Ac-DE, Ac-JE, and Ac-TE, Ac-ZEΔTM, or Ac-hsp70-efp and 72 h after infection with vAc-ZprME, vAc-ZE, vAc-DE, vAc-JE, vAc-TE, vAc-ZEΔTM, or vAc-hsp70-egfp. The arrows indicate the syncytia. (C) The number of syncytia within a field of view was counted for statistical analysis. The means and standard deviations (SD) correspond to data collected from five random fields of view.