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Proc Natl Acad Sci U S A. 1987 Dec;84(23):8540-3.

Substitution of tyrosine for either cysteine in beta-lactamase prevents release from the membrane during secretion.

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Department of Applied Biological Sciences, Massachusetts Institute of Technology, Cambridge 02139.


Six independent secretion-defective mutations were found that result in failure to release protein from the membrane into the periplasmic space of Salmonella typhimurium after removal of the signal peptide. The mutant protein is found in a membrane-bound form accessible to trypsin added to intact spheroplasts. The phenotype of these mutations supports the existence in general of an intermediate in bacterial secretion. All six mutations changed one or the other of the two cysteine residues in the mature protein to tyrosine, suggesting that these residues are involved in the release of protein into the periplasmic space, most likely by affecting protein folding.

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