Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Signal Recognition Particle”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51Linked to original sources
PubMed2000

Vaccinia expression of Mycobacterium tuberculosis-secreted proteins: tissue plasminogen activator signal sequence enhances expression and immunogenicity of M. tuberculosis Ag85.

There is increasing evidence to implicate a role for CD8(+) T cells in protective immunity against tuberculosis. Recombinant vaccinia (rVV) expressing Mycobacterium tuberculosis (MTB) proteins can be used both as tools to dissect CD8(+) T-cell responses and, in attenuated form, as candidate vaccines capable of inducing a balanced CD4(+)/CD8(+) T-cell response. A panel of rVV was constructed to express four immunodominant secreted proteins of MTB: 85A, 85B and 85C and ESAT-6. A parallel group of rVV was constructed to include the heterologous eukaryotic tissue plasminogen activator (tPA) signal sequence to assess if this would enhance expression and immunogenicity. Clear expression was obtained for 85A, 85B and ESAT-6 and the addition of tPA resulted in N-glycosylation and a 4-10-fold increase in expression. Female C57BL/6 mice were immunised using the rVV-Ag85 constructs, and interleukin-2 and gamma-interferon were assayed using a co-culture of immune splenocytes and recall antigen. There was a marked increase in cytokine production in mice immunised with the tPA-containing constructs. We report the first data demonstrating enhanced immunogenicity of rVV using a tPA signal sequence, which has significant implications for future vaccine design.

Acyltransferases↗
PubMed1999

Type III machines of Gram-negative pathogens: injecting virulence factors into host cells and more.

Many Gram-negative bacteria that cause disease in either mammals or plants share a strategy of delivering toxic proteins into the cytoplasm of host cells known as type III secretion. Recent advances have provided a glimpse at the molecular nature of these lethal injection machines. Several groups have reported fibrous structures on bacterial surfaces that appear to be extensions of type III machines and necessary for toxin injection into host cells. Other research revealed complex mechanisms of secretion substrate recognition that presumably function to direct toxins to different locations during infection.

Animals↗
PubMed2001

Ssh1p determines the translocation and dislocation capacities of the yeast endoplasmic reticulum.

Sec61p is required both for protein translocation and dislocation across the membrane of the endoplasmic reticulum (ER). However, the cellular role of the Sec61p homolog Ssh1p has not been clearly defined. We show that deltassh1 mutant cells have strong defects in both SRP-dependent and -independent translocation. Moreover, these cells were also found to be induced for the unfolded protein response and to be defective in dislocation of a misfolded ER protein. In addition, deltassh1 mutant cells rapidly became respiratory deficient. The other defects discussed above were suppressed in the respiratory-deficient state or under conditions where the rate of polypeptide translation was artificially reduced. These data identify Ssh1p as a component of a second, functionally distinct translocon in the yeast ER membrane.

Animals↗
PubMed2001

Geometric nomenclature and classification of RNA base pairs.

Non-Watson-Crick base pairs mediate specific interactions responsible for RNA-RNA self-assembly and RNA-protein recognition. An unambiguous and descriptive nomenclature with well-defined and nonoverlapping parameters is needed to communicate concisely structural information about RNA base pairs. The definitions should reflect underlying molecular structures and interactions and, thus, facilitate automated annotation, classification, and comparison of new RNA structures. We propose a classification based on the observation that the planar edge-to-edge, hydrogen-bonding interactions between RNA bases involve one of three distinct edges: the Watson-Crick edge, the Hoogsteen edge, and the Sugar edge (which includes the 2'-OH and which has also been referred to as the Shallow-groove edge). Bases can interact in either of two orientations with respect to the glycosidic bonds, cis or trans relative to the hydrogen bonds. This gives rise to 12 basic geometric types with at least two H bonds connecting the bases. For each geometric type, the relative orientations of the strands can be easily deduced. High-resolution examples of 11 of the 12 geometries are presently available. Bifurcated pairs, in which a single exocyclic carbonyl or amino group of one base directly contacts the edge of a second base, and water-inserted pairs, in which single functional groups on each base interact directly, are intermediate between two of the standard geometries. The nomenclature facilitates the recognition of isosteric relationships among base pairs within each geometry, and thus facilitates the recognition of recurrent three-dimensional motifs from comparison of homologous sequences. Graphical conventions are proposed for displaying non-Watson-Crick interactions on a secondary structure diagram. The utility of the classification in homology modeling of RNA tertiary motifs is illustrated.

Base Pairing↗
PubMed2002

Crosslinking of 4.5S RNA to the Escherichia coli ribosome in the presence or absence of the protein Ffh.

Radioactively labeled 4.5S RNA containing statistically distributed 4-thiouridine residues in place of normal uridine was prepared by T7 transcription. The ability of this modified 4.5S RNA to form a complex with the protein Ffh was demonstrated by a gel shift assay. The modified 4.5S RNA, with or without Ffh, was added to Escherichia coli ribosomes under various conditions, and crosslinking from the thiouridine residues was induced by irradiation at 350 nm. The crosslinked ribosomal components were analyzed by our standard procedures. Two clearly defined types of crosslinking were observed. The first was a crosslink to 23S rRNA, which was entirely dependent both on the presence of Ffh and a nascent protein chain in the 50S subunit. This crosslink was localized to nt approximately 2828-2837 of the 23S rRNA, from position 84 of the 4.5S molecule. The second type of crosslinking, to the 30S ribosomal subunit, was independent of the presence of Ffh, and was found both with vacant 70S ribosomes or isolated 30S subunits. Here the crosslink was localized to the 3'-terminal region of the 16S rRNA, from positions 29-50 of the 4.5S RNA. Cross-linking to ribosomal protein S1 was also observed. The known crystal structure of the protein Ffh/4.5S RNA fragment complex was extrapolated by computer modeling so as to include the whole 4.5S molecule, and this was docked onto the ribosome using the crosslinking data. The results are discussed in terms of multiple functions and binding sites of the 4.5S RNA.

Base Sequence↗
PubMed1994

Mapping critical residues in eukaryotic DNA-binding proteins: a plasmid-based genetic selection strategy with application to the Oct-2 POU motif.

Discrimination between allowed and disallowed amino acid substitutions provides a powerful method for analysis of protein structure and function. Site-directed mutagenesis allows specific hypotheses to be tested, but its systematic application to entire structural motifs is inefficient. This limitation may be overcome by genetic selection, which allows rapid scoring of thousands of randomly (or pseudorandomly) generated mutants. To facilitate structural dissection of DNA-binding proteins, we have designed two generally applicable bacterial selection systems: pPLUS selects for the ability of a protein to bind to a user-defined DNA sequence, whereas pMINUS selects against such binding. Complementary positive and negative selections allow rapid mapping of critical residues. To test and calibrate the systems, we have investigated the bipartite POU domain of the human B-cell-specific transcription factor Oct-2. (i) An invariant residue (Asn347) in the DNA-recognition helix of the POU-specific homeodomain (POUHD) was substituted by each of the 19 other possible amino acids. The mutant proteins each exhibited decreased specific DNA binding as defined in vivo by genetic selection and in vitro by gel retardation; relative affinities correlate with phenotypes in the positive and negative selection systems. An essential role for Asn347 in wild-type POUHD-DNA recognition is consistent with homologous Asn-adenine interactions in cocrystal structures of canonical homeodomains. (ii) Extension of pPLUS/pMINUS selection to the POU-specific subdomain (POUs) is demonstrated by analysis of mutations in its putative helix-turn-helix (HTH) element.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed2002

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.

Animals↗
PubMedDate not supplied

Development of a minimal cell-free translation system for the synthesis of presecretory and integral membrane proteins.

By combining translation and membrane integration/translocation systems, we have constructed a novel cell-free system for the production of presecretory and integral membrane proteins in vitro. A totally defined, cell-free system reconstituted from a minimal number of translation factors was supplemented with urea-washed inverted membrane vesicles (U-INVs) prepared from Escherichia coli, as well as with purified proteins mediating membrane targeting of presecretory and integral membrane proteins. Initially, efficient membrane translocation of a presecretory protein (pOmpA) was obtained simply by the addition of only SecA and SecB. Proteinase K digestion clearly showed the successful translocation of pOmpA inside the vesicles. Next, integration of an inner membrane protein (MtlA) into U-INVs was achieved in the presence of only SRP (Ffh) and SR (FtsY). Finally, a membrane protein possessing a large periplasmic region (FtsQ) and therefore requiring both factors (SRP/SR and SecA/SecB) for membrane integration/translocation was also shown to be integrated correctly in this cell-free system. Thus, our novel cell-free system provides not only an efficient strategy for the production of membrane-related proteins but also an improved platform for the biological study of protein translocation and integration mechanisms.

Adenosine Triphosphatases↗
PubMed2000

Alu elements and the human genome.

Alu insertional elements, the most abundant class of SINEs in humans are dimeric sequences approximately 300 bp in length derived from the 7SL RNA gene. These sequences contain a bipartite RNA pol III promoter, a central poly A tract, a 3' poly A tail, numerous CpG islands and are bracketed by short direct repeats. An estimated 500,000 to 1 x 10(6) units are dispersed throughout the human haploid genome primarily in AT rich neighborhoods located within larger GC dense chromosomal regions via a mechanism known as retroposition. Retroposition activity of Alu elements is determined by both internal and flanking regulatory elements as well as distant genes affecting transcription or transcript stability. Alu elements impact the organization and expression of the human genome at many levels including the processes of recombination, transcription and translation. Twelve subfamilies of Alu are defined by distinct patterns of diagnostic base substitutions. Subfamilies may be classified as young, intermediate or old reflecting the time since the start of retroposition by their members. Some insertions of the youngest subfamilies are not yet fixed in the human species and represent polymorphic loci. Alus are excellent molecular markers for a variety of reasons. They aid in tracing the complex pattern of duplication and rearrangements that occurred during the evolution of primate genome. Unlike other mutations, Alu sequences are rarely lost completely once retroposed, have a defined ancestral state and are free from homoplasy since independent and identical insertions are highly unlikely. Because of these characteristics, Alus are literally molecular fossils. Polymorphic Alu loci are especially useful in studies of human genetic diversity and in pedigree and forensic analysis.

Alu Elements↗
PubMed1998

U-richness is a defining feature of plant introns and may function as an intron recognition signal in maize.

Using a large set of plant gene sequences we compared individual introns to their flanking exons. Both Zea mays and Arabidopsis thaliana introns are U-rich but display no apparent bias for A. We identified fifteen 11-mer U-rich motifs as frequent elements of maize introns, and these are virtually absent from exons. By mutagenesis, we show that the single U-rich motif in the Bronze2 intron of maize plays a key role in intron processing in vivo.

Base Composition↗
PubMed2002

Late stages of protein secretion in bacilli.

This review highlights the later stages of protein secretion in bacilli, which include protein release from the membrane and their translocation through the cell wall. Mechanisms of release of secreted polypeptides into the medium differ in Gram-positive and Gram-negative bacteria due to different structure of their cell envelope. Exogenous factors including molecular chaperons that can influence polypeptide folding may be also involved in later stages of protein secretion in bacilli. In Gram-positive bacteria protein secretion also depends on structural components of the cell wall. Certain evidence exists that maintenance of the secretory function is important for normal development of the sporulation process in these bacteria.

Bacillus↗
PubMedDate not supplied

Bovine opsin has more than one signal sequence.

By deletion of selected segments from a bovine opsin complementary DNA clone and subsequent analysis of transcripts in a cell-free translation-translocation system, we have localized two out of four theoretically conceivable signal sequences required for the integration of opsin into microsomal membranes.

Amino Acid Sequence↗