Eucaryotic endoplasmic reticulum and bacterial inner cell membranes use strikingly similar mechanisms to transport proteins from one cellular compartment to another. Using a mammalian linked transcription-translation system, we show here that canine pancreatic microsomes accurately cleave off the signal sequence of β-lactamase, a secreted bacterial protein. We suggest that the apparent differences between bacterial and eukaryotic protein transport may involve only minor modulations of a profoundly conserved mechanism.

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