SUMMARY: A 19 kb I DNA fragment containing the gene for the extracellular active-site serine β-lactamase of KCC-SO352 was cloned in TK24 using the high-copy-number plasmid pIJ702 as vector. A 30-fold higher yield of β-lactamase was obtained from strain ML1, carrying the recombinant plasmid pDML51, than from grown under optimal production conditions. In all respects (molecular mass, isoelectric point, kinetics of inhibition by β-iodopenicillanate) the overproduced ML 1 β-lactamase was identical to the original enzyme. A considerable reduction of β-lactamase production was caused by elimination of a 12.8 kb portion of the 19 kb DNA fragment by cleavage at an internal I site located more than 3 kb upstream of the β-lactamase structural gene. The β-lactamase gene was located within a 1.8 NcoI-BclI fragment but when this fragment was cloned in pIJ702, the resulting strain produced hardly any more β-lactamase than the original .


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