A NEW SET OF USEFUL CLONING AND EXPRESSION VECTORS DERIVED FROM PBLUESCRIPT

A new set of cloning vectors derived from pBlueScript (Stratagene, La Jolla, CA, USA) is presented. The ampicillin-resistance-encoding gene (Ap(R)) of pBlueScript has been replaced by genes encoding resistance to either kanamycin (Km(R)) or tetracycline (Tc-R). The origin of DNA replication (ori), conferring to pBlueScript a very high-copy-number ( 500-700 copies/chromosome), has been replaced by the pBR322 ori (15-20 copies/chromosome) or the P15A ori (10-12 copies/chromosome) [Sambroo k et al.: Molecular Cloning. A Laboratory Manual, 2nd ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1989]. Therefore, eig ht new vectors with different drug selection markers and low, medium o r high plasmid copy-number were created which are compatible with each other (ColE1 ori and P15A ori) and can be selected to replace one ano ther. These vectors were further modified by the insertion of an expre ssion cassette based on the promoter and AraC repressor/activator of t he ara operon, which allows high-level expression, extremely tight reg ulation and very inexpensive induction. High-level expression of one o r two genes within the same cell is demonstrated.