Molecular architecture of the ER translocase probed by chemical crosslinking of Sss1p to complementary fragments of Sec61p

The heterotrimeric Sec6lp complex is a key component of the protein translocation apparatus of the endoplasmic reticulum membrane, The complex characterized from yeast includes Sec61p, a 10-transmembrane-domain membrane protein which has a direct interaction with Sss1p, a small C-terminal anchor protein. In order to gain some insight into the architecture of this complex we have functionally expressed Sec6lp as complementary N- and C-terminal fragments, Chemical crosslinking of Sss1p to specific Sec61p fragments in these functional combinations and suppression of sec61 mutants by over-expression of Sss1p have led to identification of the region which includes transmembrane domains TM6, TM7 and TM8 (amino acid residues L232-R406) of Sec6lp as a major site of interaction with Sss1p.