Integrative recombination of Lactobacillus delbrueckii bacteriophage mv4: functional analysis of the reaction and structure of the attP site

The integrase of the temperate bacteriophage mv4 catalyzes site-specific re combination between the phage attP site and the attB site of the host durin g lysogenization of Lactobacillus delbrueckii subsp. bulgaricus. The mv4 in tegrase also functions in a wide variety of gram-positive bacteria and in E scherichia coli. In this report, in vitro and in vivo recombination assays were developed and the integrase was purified in order to study in greater detail the mv4 attP x attB recombination event. In a cell-free extract of E . coli at 42 degrees C, the mv4 integrase promotes efficient in vitro recom bination between a supercoiled attP-containing plasmid and a linear attB fr agment. The integrase, which was purified to apparent homogeneity, showed n o absolute requirement for accessory factors, unlike the majority of the la mbda Int family of recombinases. Deletion derivatives of the attP site were constructed and tested for recombination with the attB site in vitro. A 23 4-bp DNA fragment containing five scattered putative mv4 Int-binding sites was sufficient for function of the attP site. In contrast to the right arm of attP, most of the left arm could be deleted without drastically reducing the recombination efficiency. In vivo in E. coli, mv4 Int catalyzed recomb ination in trans between attP and attB sites present on two separate plasmi ds. This property was used to confirm in vivo the results of the deletion a nalysis of the attP site performed in vitro.