Integration and excision of lambda from the chromosome occurs via a site-specific recombination process. Integration of lambda into the chromosome is catalyzed by the lambda int gene product (integrase). Integrase binds to specific sites on the phage (attP) and bacterial chromosome (attB) and catalyzes recombination between these sites. Excision of a lambda prophage from the chromosome requires the lambda int and xis (excisionase) gene products. For excision, integrase and excisionase bind to specific sites on the left (attL) and right (attR) side of the prophage and catalyze recombination between these sites. Normally the integration and excision events are efficient and precise.
Specialized transducing phage are formed by abbarent excision of a lambda lysogen. This is a very rare event compared to the normal excision via recombination between attL and attR. When the abbarent excision initially occurs, it will yield less than one specialized transducing phage per 1,000,000 wild-type phage. Thus, this lysate is called a "Low frequency transducing lysate" or LFT.
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Last modified November 26, 2003