MOLECULAR ARCHITECTURE OF THE ER TRANSLOCASE PROBED BY CHEMICAL CROSS-LINKING OF SSS1P TO COMPLEMENTARY FRAGMENTS OF SEC61P

The heterotrimeric Sec6lp complex is a key component of the protein tr anslocation apparatus of the endoplasmic reticulum membrane, The compl ex 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 archi tecture of this complex we have functionally expressed Sec6lp as compl ementary N- and C-terminal fragments, Chemical crosslinking of Sss1p t o specific Sec61p fragments in these functional combinations and suppr ession of sec61 mutants by over-expression of Sss1p have led to identi fication of the region which includes transmembrane domains TM6, TM7 a nd TM8 (amino acid residues L232-R406) of Sec6lp as a major site of in teraction with Sss1p.