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. 1993 Dec 15;268(35):26745-51.

Site-specific Photocross-Linking Reveals That Sec61p and TRAM Contact Different Regions of a Membrane-Inserted Signal Sequence

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  • PMID: 8253810
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Site-specific Photocross-Linking Reveals That Sec61p and TRAM Contact Different Regions of a Membrane-Inserted Signal Sequence

S High et al. J Biol Chem. .
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Abstract

A chemically charged amber suppressor tRNA was used to introduce the photoactivatable amino acid (Tmd)Phe at a selected position within the signal sequence of the secretory protein preprolactin. This allowed the interactions of the NH2-terminal, the central, and the COOH-terminal regions of the signal sequence to be investigated during insertion into the membrane of the endoplasmic reticulum (ER). We found that different regions of the nascent chains were photocross-linked to different ER proteins. The TRAM protein (translocating chain-associating membrane protein) contacts the NH2-terminal region of the signal sequence while the mammalian Sec61p contacts the hydrophobic core of the signal sequence and regions COOH-terminal of this. These results suggest that the ER translocation complex is composed of heterologous protein subunits which contact distinct regions of nascent polypeptides during their membrane insertion.

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