Transcriptionai induction of Streptomyces cacaoi ?-lactamase by a ?-lactam compound

Abstract
The soil bacterium Streptomyces cacaoi produces an extracellular .beta.-lactamase. The .beta.-lactamase expression could be induced by the .beta.-lactam compound 6-amino penicillinoic acid (6-APA). In liquid cultures, a 50-fold increase in .beta.-lactamase expression was observed within the first three hours after addition of 6-APA. Using the cloned .beta.-lactamase gene as a probe, it was shown that this increase was mediated at the level of transcriptional initiation. The start point of the induced .beta.-lactamase transcript was determined, and the nucleotide sequence of the promoter region was analysed. No noticeable homology was found to control regions of inducible .beta.-lactamase genes of other bacteria. A striking feature was the presence of six direct repeats (ten base pairs each) upstream of the promoter region. Thus, an example of an inducible regulatory gene system in this Gram-positive microorganism is presented. Also, the primary structure of the .beta.-lactamase was deduced, showing a high degree of homology with class A .beta.-lactamases.

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