Integration of staphylococcal phage L54a occurs by site-specific recombination: structural analysis of the attachment sites.

Lysogenization by staphylococcal phage L54a induces the loss of lipase (glycerol ester hydrolase) activity in its host Staphylococcus aureus. The attachment site of the bacterial chromosome (attB) for the phage is at the 3' end of the lipase gene, geh. The DNA fragment containing the attB (base pairs 2620-2637 inclusive) site has been sequenced. We have also cloned and determined the nucleotide sequence of the DNA fragments containing the other three attachment sites--i.e., the attP locus on the circularly permuted phage genome and the attL and attR loci at the left and right ends of the prophage in the lysogenized strain. These results reveal that an 18-base-pair core sequence is common to all four att sites. These data indicate that the crossover point must exist within the core sequence and, further, that integration is site- and orientation-specific. We also localized the viral recombinase gene to a 2.1-kilobase DNA segment extending rightward to the attP site. This region was found to be essential for integration of plasmids containing the attP site.