DNA sequences necessary for packaging of bacteriophage lambda DNA.

The extent of DNA flanking the "cohered cohesive end" site of bacteriophage lambda DNA, which is required for packaging, was determined by using defined DNA fragments and a cosmid in vivo packaging assay. From the right end of lambda DNA a 20- to 36-base-pair stretch extending from the center of the cohered cohesive ends is shown to be required, whereas the packaging efficiency of cosmids extending to 70 base pairs into the left lambda arm is reduced to 10% (compared to a fragment extending until about 80 base pairs). A 60-base-pair stretch of the left arm leaves an efficiency of only 1%. The segment thus delineated, by the nature of the assay, is both necessary and sufficient for the binding of packaging proteins to the DNA, the packaging of DNA itself, the DNA cleavage, and successful injection of the DNA into a bacterial host. By contrast, in vitro packaging of restriction fragments of mature lambda DNA directly demonstrated the selectivity of the packaging proteins for the fragment originating from the left end of the DNA. The results of the two complementary experiments are discussed in terms of the various steps before, during, and after packaging for which different sequences flanking and including the cohered cohesive ends might be required.