Integrative recombination of bacteriophage lambda: extent of the DNA sequence involved in attachment site function.

We have investigated the minimum extent of DNA sequence required for the attachment site of bacteriophage lambda to function in integrative recombination. A DNA fragment carrying the phage attachment site (attP) of bacteriophage lambda was trimmed, recloned, and tested for recombination proficiency. In order to recombine with the bacterial attachment site (attB), the phage attachment site must retain about 250 base pairs of its original sequence. On the left side, the essential sequence extends beyond 106 base pairs from the center of the 15-base-pair common core sequence but not beyond 152 base pairs. On the right side the required sequence extends beyond 68 base pairs but not beyond 99 base pairs from the center of the core. A trimmed site that has lost part of the sequence mentioned above cannot function as the phage attachment site. However, depending on which part of the sequence is present, such a site can still act in reactions normally requiring one of the prophage attachment sites or the bacterial attachment site. The results also suggest that the essential suquence of the bacterial attachment site consists only of the sequence common to the phage and bacterial attachment sites.