Nucleotide sequence of the attachment site of coliphage lambda

Abstract

MANY bacteriophages and animal viruses, as well as DNA insertion elements and transposable antibiotic resistance factors, are capable of integrating their genomes into specific sites in the genome of their hosts, giving rise to a range of important biological phenomena^1–3. This site-specific recombination reaction has been studied most extensively in bacteriophage λ (ref. 3). During the process of lysogenisation the circularised phage DNA molecule is integrated into the Escherichia coli chromosome by reciprocal exchange between a specific site in the phage DNA molecule and a specific site in the E. coli chromosome between the gal and bio operons (Fig. 1). These sites are known as attachment sites (att). The reaction is catalysed by integrase, the product of the int gene^4,5. Excision of the prophage by site-specific recombination between the prophage end attachment sites require the action of the product of the xis gene as well as that of the integrase^6,7. In order to understand the mechanism of site-specific recombination it is necessary to study the DNA–protein interactions involved. Progress has recently been made in purification and study of the integrase^8–10, and in vitro recombination systems have been developed^11,12. We report here an important step in our comprehension of the reaction at the molecular level, the determination of the DNA sequence of the λ attachment site.