(A) Histogram of average intensities in the refined P2 locations obtained from the 315 selected procapsids, indicating two populations: occupied (left curve, ~55%) and empty (right curve, ~45%). (b) Histogram of average intensities in the refined P4 locations also indicates two populations: occupied (left curve, ~28%) and empty (right curve, ~72%). (c) Histogram of intensity within the P1 shell of an individual procapsid (light grey), and the background (dark grey), overlaid with the averaged intensities of the 20 refined locations for P2 (black bars).