Secretion of staphylococcal nuclease by Bacillus subtilis

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Abstract
The staphylococcal nuclease (nuc) gene from Staphylococcus aureus was cloned and expressed in B. subtilis. The nuclease protein was expressed either from its own promoter and translation start signals, or from a combination of a B. subtilis promoter, ribosome-binding site and a signal peptide sequence. Of the active gene product, > 80% was secreted into the medium, whereas, when a signal peptide sequence was absent, as little as 4% of the nuclease activity was found in the culture medium. Intracellular (or cell-bound) nuclease, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting, was shown to have the MW of the predicted precursor protein with the signal peptide. Levels of nuclease reached 50 mg/l in the culture medium, depending on the growth medium and the strain used. These findings indicate the prospective use of nuclease as a model system for studying secretion of heterologous proteins in B. subtilis.