Sec62p, a component of the endoplasmic reticulum protein translocation machinery, contains multiple binding sites for the Sec-complex

SEC62 encodes an essential component of the Sec-complex that is responsible for posttranslational protein translocation across the membrane of the end oplasmic reticulum in Saccharomyces cerevisiae. The specific role of Sec62p in translocation was not known and difficult to identify because it is par t of an oligomeric protein complex in the endoplasmic reticulum membrane. A n in vivo competition assay allowed us to characterize and dissect physical and functional interactions between Sec62p and components of the Sec-compl ex. We could show that Sec62p binds via its cytosolic N- and C-terminal dom ains to the Sec-complex. The N-terminal domain, which harbors the major int eraction site, binds directly to the last 14 residues of Sec63p. The C-term inal binding site of Sec62p is less important for complex stability, but ad joins the region in Sec62p that might be involved in signal sequence recogn ition.