Transcriptionai induction of Streptomyces cacaoiβ-lactamase by a β-lactam compound

Summary

The soil bacterium Streptomyces cacaoi produces an extracellular β-lactamase. The β-lactamase expression could be induced by the β-lactam compound 6-amino penicillinoic acid (6-APA). In liquid cultures, a 50-fold increase in β-lactamase expression was observed within the first three hours after addition of 6-APA. Using the cloned β-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 β-lactamase transcript was determined, and the nucleotide sequence of the promoter region was analysed. No noticeable homology was found to control regions of inducible β-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 β-lactamase was deduced, showing a high degree of homology with class A β-lactamases.