The gpA-K76R mutation specifically abrogates DNA packaging activity. Sedimentation distribution profiles for the purified protomers in low salt buffer (A) and the assembled tetramer species in high salt buffer (B). WT, K76R, and a 50:50 mix of the two protomers are shown in blue, red, and violet, respectively. (C) Catalytic activity of the WT (blue) and K76R (red) terminase protomers. Error bars represent SD (n = 3).