Formation of lambda lysogens by IS2 recombination: gal operon--lambda pR promoter fusions.

When Escherichia coli carrying an IS2 element in the gal operon are infected with lambda which also carry an IS2 element, some lysogens are formed by recombination between the two insertion elements. The resulting prophage are abnormally permuted. Whereas normal prophages are bracketed by two attachment sites, the abnormal prophages carry an internal phage attachment site. Int-promoted recombination between the internal attachment site and the bacterial attachment site results in an inversion of the portion of the prophage and bacterial genome between these two sites. In addition, the expression of the gal operon in these lysogens is under the control of the prophage P_R promoter and may be used to study the factors that influence this promoter.