Abstract
The temperate bacteriophage Mu can integrate into the chromosome of
Escherichia coli in opposite orientations. Both orientations are frequent among Mu insertions in the
lacZ gene. The method for determining the prophage orientation described here can be used to orient a Mu prophage located at any site on the host chromosome and to produce F’ strains that transfer host markers in either direction from any location on the genome of
E. coli.