title: Guanosine triphosphate promotes the post-translational integration of opsin into the endoplasmic reticulum membrane.
abstract: Membrane integration of a nascent opsin polypeptide was examined to determine whether insertion of proteins into the endoplasmic reticulum is dependent upon energy provided by ribonucleotide triphosphate hydrolysis. A discrete-sized nascent chain was obtained by in vitro translation of a mRNA which lacked a termination codon yet encoded the first 156 residues of bovine opsin. Ribosomes bearing the newly synthesized opsin chains were post-translationally incubated with canine pancreas microsomal membrane vesicles after addition of exogenous ribonucleotides or ribonucleotide analogues. Post-translational membrane integration and glycosylation of the 156-residue nascent polypeptide was found to require either the presence of guanosine triphosphate or a nonhydrolyzable GTP analogue. ATP did not promote post-translational integration of the nascent polypeptide. Although ribonucleotide hydrolysis was not obligatorily required for integration of opsin, we observed an increase in the proportion of glycosylated opsin chains in post-translational incubations that contained hydrolyzable ribonucleotide triphosphates. We conclude that a GTP-binding protein performs an essential role during integration of opsin into the endoplasmic reticulum.
authors.affiliation: Department of Biochemistry, University of Massachusetts Medical School, Worcester 01655.
authors.forename: K E
authors.initials: KE
authors.lastname: Hoffman
authors.forename: R
authors.initials: R
authors.lastname: Gilmore
mesh_terms: D000818:Animals; D004285:Dogs; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D006031:Glycosylation; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D010179:Pancreas / Q000166:cytology; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism; D017299:Rod Opsins
chemical_list: D005136:Eye Proteins; D012333:RNA, Messenger; D017299:Rod Opsins; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins