Tandem duplication in bacteriophage P2: electron microscopic mapping.

The physical position of vir37, a new immunity-insensitive mutant of Escherichia coli bacteriophage P2, was mapped by the electron microscopic heteroduplex method. In P2 vir37, 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 P2 vir22, 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 P2 vir37.