Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q07644 (polypeptide)
 72,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Translocation of proteins across the endoplasmic reticulum (ER) membrane represents the first step in the eukaryotic secretory pathway. In mammalian cells, the targeting of secretory and membrane protein precursors to the ER is mediated by signal recognition particle (SRP), a cytosolic ribonucleoprotein complex comprising a molecule of 7SL RNA and six polypeptide subunits (relative molecular masses 9, 14, 19, 54, 68 and 72K). In Saccharomyces cerevisiae, a homologue of the 54K subunit (SRP54) co-purifies with a small cytoplasmic RNA, scR1 (refs 4, 5). Genetic data indicate that SRP54 and scR1 are involved in translocation in vivo, suggesting the existence of an SRP-like activity in yeast. Whether this activity requires additional components similar to those found in mammalian SRP is not known. We have recently reported a genetic selection that led to the isolation of a yeast mutant, sec65-1, which is conditionally defective in the insertion of integral membrane proteins into the ER. Here we report the cloning and sequencing of the SEC65 gene, which encodes a 31.2K protein with significant sequence similarity to the 19K subunit of human SRP (SRP19). We also report the cloning of a multicopy suppressor of sec65-1, and its identification as the previously defined SRP54 gene, providing genetic evidence for an interaction between these gene products in vivo.
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PMID:The S. cerevisiae SEC65 gene encodes a component of yeast signal recognition particle with homology to human SRP19. 131 48

We have used the homobifunctional cross-linking reagent disuccinimidyl suberate (DSS) to identify proteins that are adjacent to nascent polypeptides undergoing translocations across mammalian rough ER. Translocation intermediates were assembled by supplementing cell free translations of truncated mRNAs with the signal recognition particle (SRP) and microsomal membrane vesicles. Two prominent cross-linked products of 45 and 64 kD were detected. The 64-kD product was obtained when the cell free translation contained SRP, while formation of the 45-kD product required both SRP and translocation competent microsomal membrane vesicles. In agreement with previous investigators, we suggest that the 64-kD product arises by cross-linking of the nascent polypeptide to the 54-kD subunit of SRP. The 45-kD product resists alkaline extraction from the membrane, so we conclude that the 11-kD nascent polypeptide has been crosslinked to an integral membrane protein of approximately 34 kD (imp34). The cross-linked product does not bind to ConA Sepharose, nor is it sensitive to endoglycosidase H digestion; hence imp34 is not identical to the alpha or beta subunits of the signal sequence receptor (SSR). We propose that imp34 functions in concert with SSR to form a translocation site through which nascent polypeptides pass in traversing the membrane bilayer of the rough endoplasmic reticulum.
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PMID:ER translocation intermediates are adjacent to a nonglycosylated 34-kD integral membrane protein. 164 22

To identify some of the determinants in the 19-kilodalton protein of signal recognition particle (SRP19) for binding to signal recognition particle RNA, two mutant derivatives of the SRP19 were constructed, lacking 14 and 24 C-terminal amino acids. Polypeptides were transcribed and translated in vitro and tested for their ability to bind to signal recognition particle RNA by retention of protein-RNA complexes on DEAE-Sepharose. Both mutant polypeptides form complexes with the RNA, demonstrating that the 24 C-terminal amino acids, which include a lysine-rich sequence at positions 136-144, are dispensable. A third mutant polypeptide, in which eight additional amino acids were removed by oligonucleotide-directed digestion of the mRNA, was unable to bind. The amino acids in the sequence PKLKTRTQ correspond to positions 113-120; they are suggested to be involved in interaction with signal recognition particle RNA.
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PMID:A basic region neighboring the lysine-rich C-terminus of protein SRP19 is required for binding to signal recognition particle RNA. 172 77

The signal recognition particle (SRP) directs signal sequence specific targeting of ribosomes to the rough endoplasmic reticulum. Displacement of the SRP from the signal sequence of a nascent polypeptide is a guanosine triphosphate (GTP)-dependent reaction mediated by the membrane-bound SRP receptor. A nonhydrolyzable GTP analog can replace GTP in the signal sequence displacement reaction, but the SRP then fails to dissociate from the membrane. Complexes of the SRP with its receptor containing the nonhydrolyzable analog are incompetent for subsequent rounds of protein translocation. Thus, vectorial targeting of ribosomes to the endoplasmic reticulum is controlled by a GTP hydrolysis cycle that regulates the affinity between the SRP, signal sequences, and the SRP receptor.
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PMID:Requirement of GTP hydrolysis for dissociation of the signal recognition particle from its receptor. 185 76

The first step in the biosynthesis of secretory proteins, plasma membrane proteins, and many other proteins in a eukaryotic cell involves the transport of at least portions of the polypeptides across the endoplasmic reticulum (ER) membrane. Parts of the polypeptide chains serve as signals that direct the translocation across and the integration into the ER membrane and also determine the orientation of membrane proteins. The transport process itself may be divided into two phases: an initiation or targeting cycle, which is fairly well understood, and the actual transfer of the polypeptide chain through the membrane, the mechanism of which is still mysterious. The initiation cycle generally involves the function of the signal recognition particle (SRP) which binds to signal sequences through its 54-kDa polypeptide component, and of the SRP-receptor (docking protein) in the ER membrane whose function is dependent on GTP. The membrane transfer of the polypeptide chain appears to involve a translocation complex consisting of several membrane proteins, one of which is the signal sequence receptor protein (SSR).
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PMID:Protein transport across the endoplasmic reticulum membrane: facts, models, mysteries. 191 3

Nascent preproinsulin interacts with endoplasmic reticulum membranes after approximately 70-80 residues of the 116-amino acid precursor are polymerized (Eskridge, E. M., and Shields, D. (1983) J. Biol. Chem. 258, 11487-11491). To understand the relationship between the size of a nascent presecretory polypeptide and the efficiency of its translocation across the endoplasmic reticulum membrane, recombinant DNA molecules were generated that encoded a series of preproinsulin derivatives with the same NH2 terminus as preproinsulin and progressively shorter COOH termini. The DNA was transcribed, the in vitro transcription products were translated in the wheat germ cell-free translation system, and the interaction of the resulting truncated polypeptides with signal recognition particle (SRP) and with microsomal membranes was analyzed. Truncations composed of 78 and 64 amino acids were translocated across the endoplasmic reticulum membrane, and translocation was found to be strictly co-translational and SRP-dependent. Translocation efficiency at low membrane concentrations was reduced for these truncated molecules relative to full-length preproinsulin. Most significantly, translation of the 64-residue polypeptide was arrested by SRP after only 50 amino acids were polymerized. This suggests that the initial interaction of nascent secretory proteins with SRP occurs when only 10 residues of the signal peptide protrude from the large ribosomal subunit.
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PMID:Truncations of a secretory protein define minimum lengths required for binding to signal recognition particle and translocation across the endoplasmic reticulum membrane. 218 50

Protein transport across the endoplasmic reticulum (ER) membrane may be divided into two phases: an initiation or targeting cycle, which has been fairly well characterized, and the actual transfer of the polypeptide chain through the membrane, the mechanism of which is still unknown. In this review, the initiation cycle is discussed with emphasis on the mechanism of signal sequence recognition by the 54 kDa polypeptide of the signal recognition particle (SRP) and on the efficiency of targeting of nascent chains. Recent results are reviewed suggesting the transfer of the polypeptide chain by means of a translocation complex, a constituent of which appears to be the signal sequence receptor protein (SSR).
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PMID:Protein transport across the ER membrane. 223 46

Alu-like elements comprise the most abundant family of interspersed repetitive sequences in primates and rodents, and contain many features of processed genes, suggesting that they were initially derived by reverse transcription of processed RNA transcripts. Transcripts containing Alu family members are represented in heterologous nuclear RNAs, cytoplasmic messenger RNAs and small RNAs, although nothing is known about their function. Evolutionary studies strongly suggest that the parent RNA for the Alu-like elements is the highly conserved 7SL RNA, which is an essential component of signal recognition particle (SRP), a small cytoplasmic ribonucleoprotein whose function is the targeting of nascent secretory and membrane proteins to the rough endoplasmic reticulum (for a review see ref. 6). 7SL RNA is composed of both unique and Alu-like sequences. SRP is rod-shaped and, in addition to its RNA, contains four proteins (two monomers composed of a polypeptide of relative molecular mass (Mr) 19,000 (19K) and one of 54K, and two heterodimers, one composed of a 9K and a 14K polypeptide, and the other composed of a 68K and a 72K polypeptide, respectively). The RNA moiety is required for SRP activity, as well as for structural integrity of the particle. To investigate whether the Alu-like segments of 7SL RNA have a specific role in SRP activity, we have now purified and analysed a SRP subparticle that is created upon extensive digestion with micrococcal nuclease and entirely lacks the Alu-like sequences. We find that it contains the 72/68K, 54K and 19K proteins tightly bound, but lacks the 9/14K protein. In vitro activity assays demonstrated that the subparticle could still promote secretory protein translocation across the microsomal membrane, but could no longer trigger an arrest of pre-secretory protein synthesis. Re-addition of the 9/14K protein did not restore the elongation arrest. We conclude that the region of SRP comprised of the Alu-like RNA and the 9/14K protein exists in a distinct structural domain which is not required for the protein translocation promoted by SRP but apparently confers elongation-arresting activity on the particle.
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PMID:Removal of the Alu structural domain from signal recognition particle leaves its protein translocation activity intact. 241 65

Antibodies directed against the 68-kDa subunit of signal recognition particle (SRP) precipitate an Alu RNA X protein complex formed during in vitro transcription of a plasmid containing an Alu family sequence. The same Alu RNA X protein complex is precipitated by anti-Alu sera from certain patients with systemic lupus erythematosus and related autoimmune diseases (Kole, R., Fresco, L. D., Keene, J. D., Cohen, P. L., Eisenberg, R. A., and Andrews, P. G. (1985) J. Biol. Chem. 260, 11781-11786). Similarly to anti-SRP antibodies human, anti-Alu sera precipitate SRP from HeLa cell extract and detect a 68-kDa SRP subunit on immunoblots. These results indicate that the Alu antigen and the 68-kDa SRP subunit are the same polypeptide.
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PMID:Alu RNA transcribed in vitro binds the 68-kDa subunit of the signal recognition particle. 243 92

The signal recognition particle (SRP), which consists of the 7SL RNA molecule associated with six polypeptides ranging between 9,000 and 72,000 m.w., mediates the translocation of newly synthesized proteins across the endoplasmic reticulum. We have characterized autoantibodies that are directed against this particle from two patients with rheumatic diseases. These sera immunoprecipitated the 7SL RNA from whole extracts of HeLa cells radiolabeled with 32P, but no RNA from deproteinized cell extracts. From 35S-methionine-labeled cell extracts, they immunoprecipitated a single polypeptide of 54,000 m.w. that is consistent with a known SRP component. Sucrose density gradient studies confirmed that this protein co-migrated with the 7SL RNA, indicating the likelihood that it is physically associated with this RNA. Thus, the 54,000 m.w. SRP protein, which is essential for the SRP functions of elongation arrest and translocation, appears to be a preferential target for human autoimmune responses. Human autoantibodies that recognize the SRP should be useful adjuncts to animal antisera for studies of the structure and function of this particle.
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PMID:Characterization of human autoantibodies that selectively precipitate the 7SL RNA component of the signal recognition particle. 243 84


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