Abstract
The gene order of several independently isolated Mu prophages has been determined by deletion mapping. The prophages in which deletions were produced were located in the
lacI gene, the
lacZ gene, and the
trp operon of
Escherichia coli. The Mu deletions were tested for marker rescue against a set of sixteen Mu amber mutants. Marker rescue tests were done by constructing strains lysogenic for both cryptic Mu prophages and Mu amber mutants and then examining the resulting heterogenotes, partially diploid for Mu, for spontaneous production of wild-type Mu particles. The gene order of all Mu prophages was identical, although prophages were found in either of the two orientations with respect to the host markers. It can be inferred therefore that the temperate bacteriophage Mu, which inserts randomly into the chromosome of
E. coli, uses a specific site on its own DNA for integration.