pJC20 and pJC40--two high-copy-number vectors for T7 RNA polymerase-dependent expression of recombinant genes in Escherichia coli.

We report the construction of two plasmid vectors, pJC20 and pJC40, for the expression of recombinant genes in Escherichia coli under the control of T7 RNA polymerase. Their small sizes of ca. 2.4 kb ease the subcloning of large inserts and the high copy numbers obtained result in satisfactory yields in all plasmid preparations. A multiple-cloning site offers sites for directional cloning and nested deletions. In addition, pJC40 encodes a cleavable amino-terminal histidine tail of 10 residues which is added to the gene product, thus allowing purification by metal chelate chromatography. Observed expression yields are in the range of 10% of total bacterial protein for all genes tested in our laboratory.