A bacterial secretory protein requires signal recognition particle for translocation across mammalian endoplasmic reticulum.

In vitro transcription of DNA from plasmid pBR322 was coupled to cell-free translation in a wheat germ system. The major translation product was pre-beta-lactamase. Upon addition of dog pancreas microsomes, the precursor was processed to authentic beta-lactamase as shown by partial NH2-terminal sequence analysis. Processing was linked to translocation into the microsomal vesicles. Salt-extracted microsomes did not process pre-beta lactamase but could be reactivated by purified signal recognition particle, which is the functional component of the salt wash (Walter, P., and Blobel, G. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 7112-7116). Signal recognition particle alone caused a drastic translation arrest that could be released by salt-depleted membranes. These data are consistent with those obtained for eukaryotic proteins and suggest that co-translational translocation of both bacterial and eukaryotic secretory proteins across the endoplasmic reticulum require identical components.