The subcellular localization of beta-lactamase produced by a secretion-cloning vector pIN-III was studied by immunolabelling of frozen thin sections of Escherichia coli. Using double immuno-gold detections and internal reference proteins, it is shown here that beta-lactamase encoded by this vector can be exported and that its overproduction leads to aggregation within the periplasm. This aggregation induces the appearance of electron-dense areas immunolabelled by the antiserum directed against the beta-lactamase at the external side of the cytoplasmic membrane. The overproduced enzyme is also secreted to the medium in vesicles budding from the outer membrane of lpp strains.

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http://dx.doi.org/10.1111/j.1768-322x.1987.tb00580.xDOI Listing

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