Figure 2.

Organization of MA and CA in the membrane-bound Gag lattice. Gag domains are depicted as in Figure 1 but only MA and CA are shown. Blue, MA; light blue, HBR; and green, CA. Three types of CA-CA interactions contributing to formation of immature Gag lattice are shown on the right. The two-fold, three-fold, and six-fold interaction interfaces are denoted by pink bar, triangle, and hexagon, respectively. Six-fold interactions involving the MHR and six-helix bundle (formed by CA-CTD and SP1 regions) form Gag hexamer subunits, with interactions at the two-fold and two-fold interfaces binding adjacent hexamer rings to one another. In the immature lattice, MA trimers form above the two-fold CA interaction interface, with an MA domain presumably contributed from each of three adjacent hexamer rings.