The amino terminus of opsin translocates "posttranslationally" as efficiently as cotranslationally.
Opsin, a member of the G-protein-coupled receptor family, is a polytopic membrane protein that does not encode a cleaved amino-terminal signal sequence. The amino terminus of opsin precedes the first known targeting information, suggesting that it translocates across the endoplasmic reticulum (ER) membrane after synthesis, uncoupled from translation. However, translocation across the mammalian ER is believed to be coupled to protein synthesis. In this study we show that opsin, within a range of nascent peptide lengths, targets and translocates equally efficiently co- and posttranslationally. Longer nascent opsin peptides have a lower efficiency of cotranslational translocation but an even lower efficiency of posttranslational translocation. We also show that SRP is required for both co- and posttranslational targeting.
Kanner
Elliott M
EM
Laboratory of Cellular Biophysics, The Rockefeller University, New York, New York 10021, USA.
Klein
Irene K
IK
Friedlander
Martin
M
Simon
Sanford M
SM
D000818:Animals; D002417:Cattle; D004721:Endoplasmic Reticulum / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D010446:Peptide Fragments / Q000096:biosynthesis / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D012270:Ribosomes / Q000378:metabolism; D017299:Rod Opsins / Q000096:biosynthesis / Q000378:metabolism*; D018271:Signal Recognition Particle / Q000378:metabolism
D010446:Peptide Fragments; D017299:Rod Opsins; D018271:Signal Recognition Particle