THE SITE-SPECIFIC RECOMBINATION SYSTEM OF THE LACTOBACILLUS SPECIES BACTERIOPHAGE-A2 INTEGRATES IN GRAM-POSITIVE AND GRAM-NEGATIVE BACTERIA

The region of the bacteriophage A2 genome involved in site-specific re combination with the DNA of Lactobacillus spp. has been identified. Tw o orfs, transcribed from the same strand, have been found immediately upstream of the phage attachment site (attP). The orf adjacent to attP predicts a 385-amino-acid protein that presents significant similarit y with site-specific recombinases of the integrase family The other or f encodes a basic polypeptide of 76 amino acid residues. The junctions of the prophage with the genomes of its hosts have been determined, a llowing the identification of the host attachment site (attB), which h as a common Ig-nucleotide core region with attP. The attB site is loca ted at the 3' end of the transfer RNA(Leu) gene (anticodon CAA). Nonre plicative plasmids containing the A2-specific recombination cassette i ntegrate into different lactobacilli but also into unrelated Gram-posi tive bacteria such as Lactococcus lactis and even into Escherichia col i In Lc. lactis, integration occurs in a previously unknown intergenic region, whereas in E. coil, it maps within the rrnD operon, 5' of rrs D gene. Comparison of the integration sites in the different hosts ind icates that some flexibility is permitted in the attB sequence, since Lc. lactis and E. coil only share 13 and 11 nucleotides, respectively, with the 19-nucleotide core sequence of the lactobacilli. (C) 1998 Ac ademic Press.