Prophage lambda at unusual chromosomal locations: I. Location of the secondary attachment sites and the properties of the lysogens

Abstract

The integration, frequency of phage λ into a mutant host deleted for the normal prophage insertion site is reduced about 200-fold relative to integration into wild-type Escherichia coli. This residual integration, like normal integration, requires the int gene of the phage and occurs by a cross-over at the normal attachment site on the phage chromosome. Analysis of the resulting abnormal lysogens indicates that there are certain sites on the mutant bacterial chromosome which are preferentially utilized for prophage insertion. In addition, lysogens in which λ has inserted into or near a specific gene, thereby inactivating its function, may be obtained by the appropriate selection technique. When a bacterial gene has been inactivated by prophage integration, prophage excision can restore its function. Prophage excision from the abnormal sites is inefficient but, like excision from the normal site, it requires two phage genes: int and xis. In this respect the abnormal bacterial attachment sites resemble the normal bacterial attachment site rather than a phage or a hybrid attachment site. The abnormal lysogens are of value for deletion mapping of various portions of the E. coli chromosome and for the production of novel types of transducing phages.