Figure 8.

Proposed model for nuclease regulation. During ‘translocation mode’ the nuclease domain active site is sequestered from DNA by interactions of the TerL with portal and capsid, preventing premature cleavage. The ATPase domain serves as the sole surface for gripping DNA during packaging. Upon completion of packaging TerL enters ‘cleavage mode’. TerL dissociates from the portal and capsid, releasing the inhibition of the nuclease domains. The ATPase domains remains tightly bound to DNA. The nuclease domains rearrange to cleave each of the antiparallel DNA strands. Although depicted as a blunt cut, cleavage could also leave overhangs depending on how both nuclease domains engage DNA.