Versatile cloning vectors derived from the runaway-replication plasmid pKN402.

Two cloning vectors have been constructed employing runaway-replication mutants of plasmid R1. One of these, pMOB45, carries tetracycline and chloramphenicol resistance. The other, pMOB48, carries chloramphenicol resistance, lacOP, and an assayable part of the lacPOZ operon. Both of these plasmids can be amplified to high levels by heat induction, which condition does not lead to inhibition of protein synthesis; thus the plasmid can produce large amounts of DNA and protein. In pMOB48, a unique BamHI site is present near the amino-terminus of the beta-galactosidase gene. Chimeras formed by the insertion of restriction fragments at this site can be detected on X-gal plates, and can be used for the lacIq-controlled expression of proteins which are fused to the amino-terminus of beta-galactosidase. Induction with IPTG at 40 degrees C leads to the synthesis of extremely high levels of proteins whose gene have been cloned into this site.