Signal peptidase and oligosaccharyltransferase interact in a sequential and dependent manner within the endoplasmic reticulum.

We demonstrate that the signal peptides of prepro-alpha-factor and preinvertase must be cleaved before Asn-X-Ser/Thr acceptor tripeptides located near the signal peptides of these precursors can be efficiently glycosylated within the endoplasmic reticulum of the yeast Saccharomyces cerevisiae. The data support a model whereby the interaction of a signal peptide with the membrane prevents an acceptor tripeptide juxtaposed to the signal peptide from accessing the oligosaccharyltransferase active site until the signal peptide is cleaved.