Fig. 1

a Schematic diagram of the HIV-1 Gag sequential cleavage and virus maturation process. RNA was omitted for clarity. b CA–SP1 cleavage. The ribbon diagram of the CA monomer is shown with the CypA loop and MHR highlighted in orange and the SP1 region depicted as a dotted blue line. The T8I mutation in SP1 mimics the presence of maturation inhibitors (MI) in abolishing SP1 cleavage. c A cryo-EM image of CA–SP1 tubular assemblies. Scale bar, 50 nm. d–h Cryo-EM reconstruction of CA–SP1 assemblies. d Surface rendering of the of CA–SP1 3D density map, low-pass filtered to 8 Å resolution. The density map (contoured at 2σ) is colored in orange and blue for CA–CTD and CA–NTD, respectively, viewed along (top) and perpendicular to (bottom) the tube axis. e MDFF fitting of three CA hexamers (PDB code 4XFX, gold, magenta, and blue ribbons) into the density map. f Superposition of the ribbon diagrams of three CA molecules at the trimer interface (green, PDB code 3j34) onto the equivalent model for the CA–SP1 trimer interface (gold, magenta, and blue). g, h Comparison of the dimer (g) and trimer (h) interfaces in CA assemblies (green) to those in CA–SP1 assemblies (gold, magenta, blue). i The variabilities among the six CA molecules in CA (top) and CA–SP1 (bottom) assemblies. j Assembly assay of CA–SP1(T8I) NL4-3 and CA NL4-3 for different concentrations of NaCl. k TEM images of tubular assemblies of CA(A92E) and CA(A92E)–SP1 variants