Translocation and specific cleavage of bacteriophage T7 DNA in vivo by EcoKI

Infection of Escherichia coli containing the type I restriction enzyme EcoK I by bacteriophage T7 0.3 mutants leads to restriction during the late stag es of genome entry and during DNA replication, Patterns of cleavage in vivo suggest that some cutting occurs near the midpoint of two recognition site s, consistent with the idea that EcoKI translocates DNA bidirectionally thr ough itself and cuts when two enzyme molecules collide. Rapid ejection of a 0.3(+) T7 genome from a bacteriophage lambda particle results in degradati on of the infecting DNA by EcoKI, showing that the normal T7 DNA translocat ion process delays restriction. A unique recognition site inserted at the g enomic left end allows EcoKI to function as a molecular motor and to transl ocate the remaining 39 kilobases of T7 DNA into the cell.