Serotype F double- and triple-converting phage insertionally inactivate the Staphylococcus aureus beta-toxin determinant by a common molecular mechanism.

The precise molecular mechanism of Staphylococcus aureus beta-toxin inactivation by the serotype F triple-converting phage phi 42, phi A1 and phi A3 was investigated. Sequence analysis of the phi 42 (attP) and Staphylococcus aureus (attB) attachment sites and the left (attL) and right (attR) chromosomal/bacteriophage DNA junctions of individual lysogens, each harbouring a triple-converting phage, revealed the presence of a common 14-bp core sequence in all four sites. These findings indicate that the genomes of the triple-converting phage integrate into the 5'-end of the beta-toxin gene (hlb) by a site- and orientation-specific mechanism identical to that previously described for the serotype F double-converting phage phi 13.