(a) Primary structure of the Ebola virus Gp. The numbers indicate amino acid positions (including the signal peptide) for (i) potential carbohydrate sites (4), (ii) the cleavage of Gp into Gp1 and Gp2 occurring at position 501 (5, 6); and (iii) Gp2 anchoring in the membrane by amino acids 651–672. The sequence of the expressed construct pIIGp2(552–650) is shown with the a and d heptad positions of pIIGCN4 in-frame with the predicted a and d positions of the Ebola virus TM protein (14). The cysteines (601 and 608) involved in disulfide formation are indicated and those changed to Ser (556 and 609) are indicated by S. (b) Chemical crosslinking of pIIGp2(552–650). Crosslinked products were separated on 15% SDS/PAGE and bands are stained with Coomassie brilliant blue. Lane 1, not reduced; lane 2, reduced; lanes 3–6 with ethyleneglycol bis(-succinimidylsuccinate) crosslinking concentrations of 0.1, 0.5, 2.0, and 5.0 mM. Molecular weight standards are shown. Bands corresponding to monomer, dimer, and trimer are indicated.