Tandem Duplication in Bacteriophage P2: Electron Microscopic Mapping

The physical position ofvir37 , a new immunity-insensitive mutant ofEscherichia coli bacteriophage P2, was mapped by the electron microscopic heteroduplex method. In P2vir37 , a segment equivalent to 2.8% of P2 DNA is added. The addition was characterized as a tandem duplication of the segment occurring between 77.2 and 80.0% from the left end of P2 DNA (the right half of P2 DNA is arbitrarily defined, from denaturation map studies, as the half richer in A + T). The point of addition of the duplicated segment (the “novel-joint”) was, thus, 80.0% from the left end of P2 DNA. On the basis of previous studies on P2vir22 , it was tentatively concluded that the physical and genetic maps of P2 are colinear. This conclusion is now further supported by physical and genetic data on P2vir37 .