attB

a bacterial attachment site that in the E. coli chromosome consists of a core of approx. 25 bp located between the gal and bio genes. In addition there are a number of secondary sites. Bacteriophage lambda DNA is integrated at this site through its attachment site attP (243 bp) in a reaction catalysed by the phage-encoded integrase (Int) and the integration host factor (IHF). On integration the prophage is bounded on its left side by the attL site, and on the right side by the attR site. Excision of the prophage takes place by recombination at the attL and attR sites in a reaction catalysed by Int, IHF, and excisionase (Xis). This recreates the attB site in the bacterial chromosome and the attP site in lambda DNA. attB and attP sites are used in plasmid vectors designed from cloning by site-specific recombination.

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