Fig. 1: Cryo-ET of immature HTLV-1 Gag VLPs.

a, Computational slice (thickness, 8.8 nm) through a cryo-electron tomogram containing HTLV-1 Gag-based VLPs. Protein density is black. Scale bar, 50 nm. The shown tomogram is representative of the 85 tomograms acquired. b, Enlarged view of the Gag lattice within VLPs, as annotated by a white rectangle in a. The arrowheads designate the different layers of the radially aligned Gag lattice underneath the viral membrane (VM): NC-RNP (1), CA-CTD (2), CA-NTD (3), MA (4), inner leaflet (5) and outer leaflet (6). c, The 1D radial density plot of the Gag lattice in immature HTLV-1 Gag-based VLPs. Two zero-value reference points are reported for the distance measurement. The primary x axis reference zero value is set at the VM (top x axis). The secondary x axis reference zero value is set at the local density minimum between the CA-NTD and CA-CTD (bottom x axis) and is provided to allow a straightforward comparison to Fig. 2c. The distance of the different layers from these reference points is given in nanometers. The annotation with arrowheads is as in b. AU, arbitrary units. d–f, Isosurface representations of the subtomogram average of the CA hexamer from HTLV-1 Gag-based VLPs. The CA-NTDs of the central hexamer are colored cyan, with one monomer highlighted in blue. Two additional CA-NTD monomers from adjacent hexamers are also colored in cyan, to highlight the trimeric interhexamer interface. The CA-CTDs of the central hexamer are colored orange and red. The hexameric arrangement is indicated by a small hexagon. d, CA lattice as seen from the outside of the VLP and rotated by 90° to show a side view. e, Top view of the CA-NTD, with the trimeric interhexamer interface and the intrahexameric interface indicated with a dashed red triangle and dashed yellow hexagon, respectively. CA monomers in the trimeric interhexamer interface are annotated with I, II and III. f, Top view of the CA-CTD hexamer. A dashed orange ellipsoid highlights one CA-CTD dimer linking adjacent hexamers. g,h, Molecular models of the CA-NTD and CA-CTD rigid-body fitted into the EM density of the immature CA lattice. Coloring as in d–f. g, Trimeric CA-NTD interactions linking hexamers, involving residues spanning helices 4 and 5. h, Interactions around the hexamer, involving helices 1, 2 and 3 from adjacent CA-NTDs. i, Model of the CA-CTD dimer.