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Isolation and characterization of cDNA clones for rat ribophorin I: complete coding sequence and in vitro synthesis and insertion of the encoded product into endoplasmic reticulum membranes.

Authors: Harnik-Ort, V  Prakash, K  Marcantonio, E  Colman, DR  Rosenfeld, MG  Adesnik, M  Sabatini, DD  Kreibich, G 
Citation: Harnik-Ort V, etal., J Cell Biol 1987 Apr;104(4):855-63.
Pubmed: (View Article at PubMed) PMID:3031084

Ribophorins I and II are two transmembrane glycoproteins that are characteristic of the rough endoplasmic reticulum and are thought to be part of the apparatus that affects the co-translational translocation of polypeptides synthesized on membrane-bound polysomes. A ribophorin I cDNA clone containing a 0.6-kb insert was isolated from a rat liver lambda gtll cDNA library by immunoscreening with specific antibodies. This cDNA was used to isolate a clone (2.3 kb) from a rat brain lambda gtll cDNA library that contains the entire ribophorin I coding sequence. SP6 RNA transcripts of the insert in this clone directed the in vitro synthesis of a polypeptide of the expected size that was immunoprecipitated with anti-ribophorin I antibodies. When synthesized in the presence of microsomes, this polypeptide, like the translation product of the natural ribophorin I mRNA, underwent membrane insertion, signal cleavage, and co-translational glycosylation. The complete amino acid sequence of the polypeptide encoded in the cDNA insert was derived from the nucleotide sequence and found to contain a segment that corresponds to a partial amino terminal sequence of ribophorin I that was obtained by Edman degradation. This confirmed the identity of the cDNA clone and established that ribophorin I contains 583 amino acids and is synthesized with a cleavable amino terminal insertion signal of 22 residues. Analysis of the amino acid sequence of ribophorin I suggested that the polypeptide has a simple transmembrane disposition with a rather hydrophilic carboxy terminal segment of 150 amino acids exposed on the cytoplasmic face of the membrane, and a luminal domain of 414 amino acids containing three potential N-glycosylation sites. Hybridization measurements using the cloned cDNA as a probe showed that ribophorin I mRNA levels increase fourfold 15 h after partial hepatectomy, in confirmation of measurements made by in vitro translation of liver mRNA. Southern blot analysis of rat genomic DNA suggests that there is a single copy of the ribophorin I gene in the haploid rat genome.


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CRRD Object Information
CRRD ID: 729694
Created: 2003-11-26
Species: All species
Last Modified: 2004-05-25
Status: ACTIVE


RGD is funded by grant HL64541 from the National Heart, Lung, and Blood Institute on behalf of the NIH.