Prophage deletion mapping of bacteriophage Mu-1

Abstract

Bacteriophage Mu integrates at a very large number of sites which appear to be randomly distributed over the whole Escherichia coli chromosome ( Taylor, 1963) and even within a single gene, lacZ ( Bukhari and Zipser, 1972; Daniell et al., 1972 ). In order to determine whether integration also occurs at many sites on the Mu chromosome, deletion mapping of the Mu prophage was done in seven independently isolated lysogens in which the Mu prophages were located in leu, trp, or lys. The deletion strains were isolated as strains which had simultaneously become defective for phage production and for the function of a gene close to the prophage. Mapping of the prophage in these deletion strains was done by marker rescue using Mu amber mutants from eighteen complementation groups. Since the prophage map obtained is the same in all seven lysogens, it is clear that the integration of Mu does not occur randomly over the Mu chromosome. For the three prophages in leu the deletions entering the prophage from the arabinose operon remove different ends of the prophage in the different lysogens. This indicates that the prophage may be oriented in either direction in a given operon.