pL1 to pL6 plasmid subclones derived from phage lambda. To construct the pL series of subclones, lambda DNA was digested with BamHI and cloned into the BamHI site of pMECA. The subclones are shown here after digestion with BamHI. Lane M, 1 kb ladder; lanes 1–6, pL1–pL6. Lanes 2–5 show both the inserts (16.8, 5.6, 6.5, 7.2 kb, respectively) and the pMECA vector (2.8 kb). Plasmids pL1 and pL6 (5.8 and 7.2 kb inserts, respectively) contain a single BamHI site and include the end clones of phage lambda.