A second site-specific recombination event in the lambdoid bacteriophage HK022

An in vitro site-specific recombination reaction of the lambdoid phage HK022 has revealed two supercoiled products that proved to be Holliday intermediates. One of them is the Holliday intermediate which has resulted from an attP × attB reaction. The other is an intermediate which has resulted from a recombination reaction between attP and the attL site of the product from the first reaction. The preferential attL × attP over attR × attP reaction was confirmed in vitro and in vivo by challenging attP sites with attL and attR sites. The biased attP × attL over attP × attR reaction in phage HK022 is discussed.