title: The signal sequence receptor, unlike the signal recognition particle receptor, is not essential for protein translocation.
abstract: Detergent extracts of canine pancreas rough microsomal membranes were depleted of either the signal recognition particle receptor (SR), which mediates the signal recognition particle (SRP)-dependent targeting of the ribosome/nascent chain complex to the membrane, or the signal sequence receptor (SSR), which has been proposed to function as a membrane bound receptor for the newly targeted nascent chain and/or as a component of a multi-protein translocation complex responsible for transfer of the nascent chain across the membrane. Depletion of the two components was performed by chromatography of detergent extracts on immunoaffinity supports. Detergent extracts lacking either SR or SSR were reconstituted and assayed for activity with respect to SR dependent elongation arrest release, nascent chain targeting, ribosome binding, secretory precursor translocation, and membrane protein integration. Depletion of SR resulted in the loss of elongation arrest release activity, nascent chain targeting, secretory protein translocation, and membrane protein integration, although ribosome binding was unaffected. Full activity was restored by addition of immunoaffinity purified SR before reconstitution of the detergent extract. Surprisingly, depletion of SSR was without effect on any of the assayed activities, indicating that SSR is either not required for translocation or is one of a family of functionally redundant components.
authors.affiliation: Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York 10021-6399.
authors.forename: G
authors.initials: G
authors.lastname: Migliaccio
authors.forename: C V
authors.initials: CV
authors.lastname: Nicchitta
authors.forename: G
authors.initials: G
authors.lastname: Blobel
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000302:isolation & purification; D002135:Calcium-Binding Proteins; D002417:Cattle; D004285:Dogs; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009842:Oligopeptides / Q000138:chemical synthesis / Q000276:immunology; D010179:Pancreas / Q000378:metabolism*; D010441:Peptide Chain Elongation, Translational; D011388:Prolactin / Q000235:genetics*; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000235:genetics*; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000032:analysis / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; D012270:Ribosomes / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D000906:Antibodies; D002135:Calcium-Binding Proteins; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D009842:Oligopeptides; D011498:Protein Precursors; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; C036318:signal peptide receptor; C066973:signal sequence receptor; C017671:preprolactin; D011388:Prolactin