Figure 4.

Residues Met195 and Phe259 are critical for function. (A) SDS-polyacrylamide gel showing the purity of gp17 proteins. Note that the full-length protein was non-specifically cleaved at the C-terminus to produce 2–3 shorter bands. All the species retained DNA packaging activity. (B) in vivo nuclease activity assays. The numbers ‘0’ and ‘3’ at the top of the lanes represent hours after induction with IPTG. (C) ATPase assays. (D) in vitro DNA packaging assays. Upper arrow represents a small amount of DNA associated with the heads. Lower arrow represents the packaged DNA. The vertical lines between the panels A and D indicate the gp17 protein used in each assay, as shown at the top of panels A and D. The lanes corresponding to the ATPase and DNA packaging activities of WT or mutant gp17 lanes in panels C and D represent duplicate assays. The black lines within a panel indicate the boundaries of the sliced and pasted lanes. This was done to maintain the same order going from panel A to panel D. See Supplementary Materials and Methods for details.