Fig. 7.

Proposed model for the mechanism of DNA translocation by TerL. (A) TerL ring is shown as in Fig. 6F. The nuclease domains interact with the portal complex (translucent gray rectangle) and possibly the procapsid (black curve). DNA is not shown but interacts with TerL through the DNA interaction motif (Arg101). Each subunit’s lid is bound tightly to the Rossmann fold of the adjacent subunit. (B) Upon ATP hydrolysis and release by the magenta subunit, the lid stays bound to the blue subunit and the Rossmann fold rotates 13° upward. To allow for this movement, the adjacent red subunit must also move in concert with the magenta subunit. To represent that the second site of symmetry breaking is unknown, the other three ATPase domains are faded. After hydrolyzing ATP, the magenta subunit releases DNA to the red subunit to translocate DNA upward through the pore; into the pore of the portal complex; and, ultimately, inside the procapsid. The release of DNA at each cycle by the ATP-hydrolyzing subunit allows for unidirectional DNA translocation.