The T = 4 capsids were analysed, and class averages were calculated for the twofold, threefold and fivefold axes of symmetry. A preliminary icosahedral 3D model was visually inspected using the Chimera software package [15] . Data were then analysed using projection matching [14, 16] . Between each refinement cycle the software package SITUS [17] was used in parallel to select the contiguous mass which corresponded to a single T = 4 HBV/G capsid.