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PubMed2003

Empirical models for substitution in ribosomal RNA.

Empirical models of substitution are often used in protein sequence analysis because the large alphabet of amino acids requires that many parameters be estimated in all but the simplest parametric models. When information about structure is used in the analysis of substitutions in structured RNA, a similar situation occurs. The number of parameters necessary to adequately describe the substitution process increases in order to model the substitution of paired bases. We have developed a method to obtain substitution rate matrices empirically from RNA alignments that include structural information in the form of base pairs. Our data consisted of alignments from the European Ribosomal RNA Database of Bacterial and Eukaryotic Small Subunit and Large Subunit Ribosomal RNA ( Wuyts et al. 2001. Nucleic Acids Res. 29:175-177; Wuyts et al. 2002. Nucleic Acids Res. 30:183-185). Using secondary structural information, we converted each sequence in the alignments into a sequence over a 20-symbol code: one symbol for each of the four individual bases, and one symbol for each of the 16 ordered pairs. Substitutions in the coded sequences are defined in the natural way, as observed changes between two sequences at any particular site. For given ranges (windows) of sequence divergence, we obtained substitution frequency matrices for the coded sequences. Using a technique originally developed for modeling amino acid substitutions ( Veerassamy, Smith, and Tillier. 2003. J. Comput. Biol. 10:997-1010), we were able to estimate the actual evolutionary distance for each window. The actual evolutionary distances were used to derive instantaneous rate matrices, and from these we selected a universal rate matrix. The universal rate matrices were incorporated into the Phylip Software package ( Felsenstein 2002. http://evolution.genetics.washington.edu/phylip.html), and we analyzed the ribosomal RNA alignments using both distance and maximum likelihood methods. The empirical substitution models performed well on simulated data, and produced reasonable evolutionary trees for 16S ribosomal RNA sequences from sequenced Bacterial genomes. Empirical models have the advantage of being easily implemented, and the fact that the code consists of 20 symbols makes the models easily incorporated into existing programs for protein sequence analysis. In addition, the models are useful for simulating the evolution of RNA sequence and structure simultaneously.

Amino Acid Substitution↗
PubMed1992

Characterization of a 7-kilodalton subunit of vaccinia virus DNA-dependent RNA polymerase with structural similarities to the smallest subunit of eukaryotic RNA polymerase II.

A previously unrecognized 7-kDa polypeptide copurified with the DNA-dependent RNA polymerase of vaccinia virus virions. Internal amino acid sequences of the small protein matched a viral genomic open reading frame of 63 codons. Antipeptide antiserum was used to confirm the specific and complete association of the 7-kDa protein with RNA polymerase. The amino acid sequence predicted from the viral gene, named rpo7, was 23% identical to that of the smallest subunit of Saccharomyces cerevisiae RNA polymerase II, and a metal-binding motif, Cys-X-X-Cys-Gly, was located at precisely the same location near the N terminus in the two proteins. RNA analyses demonstrated early transcriptional initiation and termination signals in the rpo7 gene sequence. The viral RNA polymerase subunit was synthesized during the early phase of infection and continued to accumulate during the late phase.

Amino Acid Sequence↗
PubMed2006

The internal transcribed spacer 2 database--a web server for (not only) low level phylogenetic analyses.

The internal transcribed spacer 2 (ITS2) is a phylogenetic marker which has been of broad use in generic and infrageneric level classifications, as its sequence evolves comparably fast. Only recently, it became clear, that the ITS2 might be useful even for higher level systematic analyses. As the secondary structure is highly conserved within all eukaryotes it serves as a valuable template for the construction of highly reliable sequence-structure alignments, which build a fundament for subsequent analyses. Thus, any phylogenetic study using ITS2 has to consider both sequence and structure. We have integrated a homology based RNA structure prediction algorithm into a web server, which allows the detection and secondary structure prediction for ITS2 in any given sequence. Furthermore, the resource contains more than 25,000 pre-calculated secondary structures for the currently known ITS2 sequences. These can be taxonomically searched and browsed. Thus, our resource could become a starting point for ITS2-based phylogenetic analyses and is therefore complementary to databases of other phylogenetic markers, which focus on higher level analyses. The current version of the ITS2 database can be accessed via http://its2.bioapps.biozentrum.uni-wuerzburg.de.

DNA, Ribosomal Spacer↗
PubMed1996

Functions of the 5' leader of murine leukemia virus genomic RNA in virion structure, viral replication and pathogenesis, and MLV-derived vectors.

Retroviruses are a family of widespread small animal viruses that can cause a variety of neoplastic and immunosuppressive diseases. Murine leukemia viruses (MuLV) have been used as model systems to investigate virion and genomic RNA structure, viral replication and variability, and pathogenesis. Detailed knowledge of the genetic structure of MuLV and of the viral life cycle has led to the development of MuLV-derived retroviral vectors for gene transfer with potential applications in human gene therapy. In this review we have summarized the properties and functions of the 5' domain, called the leader, of MuLV genomic RNA. The 5' leader is formed of small interspersed and superimposed genetic elements involved in every step of the viral life cycle. In addition, the 3' domain of the leader encodes the N-terminal part of glycosylated forms of the GAG polyprotein, also named Gross cell surface antigen (GCSA or glycoGAG) which is essential for full spreading and pathogenic abilities of the virus in the animal. Therefore, the 5' leader of MuLV genomic RNA appears to be a very attractive model to study structure-function relationships of a small and multifunctional genetic domain in vitro, in cell culture and in the animal.

Gene Transfer Techniques↗
PubMed1985

Lipopolysaccharide and polyribonucleotide activation of macrophages: implications for a natural triggering signal in tumor cell killing.

There is evidence that activation of macrophages for tumor cell killing can involve either two signals (interferon/lipopolysaccharide, for example) or one signal (lipopolysaccharide or double-stranded RNA, for example). We investigated the apparent one-signal activation of bone marrow-derived macrophages for P815 mastocytoma killing by treatment with lipopolysaccharide (LPS) or by the synthetic double-stranded polyribonucleotide polyinosinic acid-polycytidylic acid (poly I:C). We found that "direct" activation of macrophages by either LPS or poly I:C was still a two-signal process. Based on antibody neutralizations, the first signal was probably mediated by LPS or poly I:C induced alpha/beta interferon in the macrophage cultures, and the second signal was that of a direct effect of the LPS or poly I:C on the cell. The fact that poly I:C can provide the triggering signal for macrophage activation suggests a possible role for double-stranded RNA structures in macrophage triggering. Such double-stranded RNA requirements could be met by single-stranded RNAs that possess significant double-strandedness in their structures.

Animals↗
PubMed1999

Probing ribosome structure by europium-induced RNA cleavage.

Divalent metal ions are absolutely required for the structure and catalytic activities of ribosomes. They are partly coordinated to highly structured RNA, which therefore possesses high-affinity metal ion binding pockets. As metal ion induced RNA cleavages are useful for characterising metal ion binding sites and RNA structures, we analysed europium (Eu3+) induced specific cleavages in both 16S and 23S rRNA of E. coli. The cleavage sites were identified by primer extension and compared to those previously identified for calcium, lead, magnesium, and manganese ions. Several Eu3+ cleavage sites, mostly those at which a general metal ion binding site had been already identified, were identical to previously described divalent metal ions. Overall, the Eu3+ cleavages are most similar to the Ca2+ cleavage pattern, probably due to a similar ion radius. Interestingly, several cleavage sites which were specific for Eu3+ were located in regions implicated in the binding of tRNA and antibiotics. The binding of erythromycin and chloramphenicol, but not tetracycline and streptomycin, significantly reduced Eu3+ cleavage efficiencies in the peptidyl transferase center. The identification of specific Eu3+ binding sites near the active sites on the ribosome will allow to use the fluorescent properties of europium for probing the environment of metal ion binding pockets at the ribosome's active center.

Anti-Bacterial Agents↗
PubMed2000

Theoretical design of antisense genes with statistically increased efficacy.

Endogenous expression of antisense RNA represents one major way of applying antisense nucleic acids. To express antisense RNA intracellularly, recombinant antisense genes have to be designed and introduced into cells where the target RNA is encountered. Efficient annealing between the antisense RNA and the target RNA is crucial for efficacy and is strongly influenced by RNA structure. Here we extend structural rules for the design of in vitro transcribed antisense RNAs to the design of recombinant antisense genes. Intracellularly expressed antisense RNA transcripts contain a central antisense portion and additional flanking vector-derived sequences. A computer algorithm was generated to compose large sets of antisense genes, to calculate secondary structures of the transcribed sequences and to select for favorable structures of antisense RNA in terms of annealing and efficacy. The biological test system to measure efficiency of antisense genes was human immunodeficiency virus type 1 (HIV-1) replication in 293T cells. When considering the lower intracellular steady-state levels of favorably structured endogenous transcripts, an antisense effect against HIV-1 replication was observed that was up to 60-fold stronger than that measured for predicted unfavorable species. The computational selection was successful for antisense portions of 300 nt but not 100 nt in length. This theoretical design of antisense genes supports their improved application under time- and labor-saving conditions.

Algorithms↗
PubMed1998

Adenovirus VAI RNA antagonizes the RNA-editing activity of the ADAR adenosine deaminase.

The virus-associated VAI RNA of adenovirus is a small highly structured RNA that is required for the efficient translation of cellular and viral mRNAs at late times after infection. VAI RNA antagonizes the activation of the interferon-inducible RNA-dependent protein kinase, PKR, an important regulator of translation. The RNA-specific adenosine deaminase, ADAR, is an interferon-inducible RNA-editing enzyme that catalyzes the site-selective C-6 deamination of adenosine to inosine. ADAR possesses three copies of the highly conserved RNA-binding motif (dsRBM) that are similar to the two copies found in PKR, the enzyme in which the prototype dsRBM motif was discovered. We have examined the effect of VAI RNA on ADAR function. VAI RNA impairs the activity of ADAR deaminase. This inhibition can be observed in extracts prepared from interferon-treated human cells and from monkey COS cells in which wild-type recombinant ADAR was expressed. Analysis of wild-type and mutant forms of VA RNA suggests that the central domain is important in the antagonism of ADAR activity. These results suggest that VAI RNA may modulate viral and cellular gene expression by modulating RNA editing as well as mRNA translation.

Adenosine Deaminase↗
PubMed2006

The architectonics of programmable RNA and DNA nanostructures.

The past several years have witnessed the emergence of a new world of nucleic-acid-based architectures with highly predictable and programmable self-assembly properties. For almost two decades, DNA has been the primary material for nucleic acid nanoconstruction. More recently, the dramatic increase in RNA structural information led to the development of RNA architectonics, the scientific study of the principles of RNA architecture with the aim of constructing RNA nanostructures of any arbitrary size and shape. The remarkable modularity and the distinct but complementary nature of RNA and DNA nanomaterials are revealed by the various self-assembly strategies that aim to achieve control of the arrangement of matter at a nanoscale level.

Base Sequence↗
PubMed1994

Synthesis of circular RNA in bacteria and yeast using RNA cyclase ribozymes derived from a group I intron of phage T4.

Studies on the function of circular RNA and RNA topology in vivo have been limited by the difficulty in expressing circular RNA of desired sequence. To overcome this, the group I intron from the phage T4 td gene was split in a peripheral loop (L6a) and rearranged so that the 3' half intron and 3' splice site are upstream and a 5' splice site and 5' half intron are downstream of a single exon. The group I splicing reactions excise the internal exon RNA as a circle (RNA cyclase ribozyme activity). We show that foreign sequences can be placed in the exon and made circular in vitro. Expression of such constructs (RNA cyclase ribozymes) in Escherichia coli and yeast results in the accumulation of circular RNA in these organisms. In yeast, RNA cyclase ribozymes can be expressed from a regulated promoter like an mRNA, containing 5' leader and 3' trailer regions, and a nuclear pre-mRNA intron. RNA cyclase ribozymes have broad application to questions of RNA structure and function including end requirements for RNA transport or function, RNA topology, efficacy of antisense or ribozyme gene control elements, and the biosynthesis of extremely long polypeptides.

Bacteriophage T4↗
PubMed2006

Quadruplex DNA: sequence, topology and structure.

G-quadruplexes are higher-order DNA and RNA structures formed from G-rich sequences that are built around tetrads of hydrogen-bonded guanine bases. Potential quadruplex sequences have been identified in G-rich eukaryotic telomeres, and more recently in non-telomeric genomic DNA, e.g. in nuclease-hypersensitive promoter regions. The natural role and biological validation of these structures is starting to be explored, and there is particular interest in them as targets for therapeutic intervention. This survey focuses on the folding and structural features on quadruplexes formed from telomeric and non-telomeric DNA sequences, and examines fundamental aspects of topology and the emerging relationships with sequence. Emphasis is placed on information from the high-resolution methods of X-ray crystallography and NMR, and their scope and current limitations are discussed. Such information, together with biological insights, will be important for the discovery of drugs targeting quadruplexes from particular genes.

Animals↗
PubMedDate not supplied

Statistical analysis of RNA backbone.

Local conformation is an important determinant of RNA catalysis and binding. The analysis of RNA conformation is particularly difficult due to the large number of degrees of freedom (torsion angles) per residue. Proteins, by comparison, have many fewer degrees of freedom per residue. In this work, we use and extend classical tools from statistics and signal processing to search for clusters in RNA conformational space. Results are reported both for scalar analysis, where each torsion angle is separately studied, and for vectorial analysis, where several angles are simultaneously clustered. Adapting techniques from vector quantization and clustering to the RNA structure, we find torsion angle clusters and RNA conformational motifs. We validate the technique using well-known conformational motifs, showing that the simultaneous study of the total torsion angle space leads to results consistent with known motifs reported in the literature and also to the finding of new ones.

Base Sequence↗
PubMed2004

A general method for rapid and nondenaturing purification of RNAs.

A key bottleneck in RNA structural studies is preparing milligram quantities of RNA, and current techniques have changed little in over a decade. To address this, we have developed an affinity tag-based purification method of RNA oligonucleotides. The tag is attached to the 3'-end of almost any desired RNA sequence, allowing for the rapid and specific removal of the RNA of interest directly from in vitro transcription reactions using an affinity column to which a specific RNA-binding protein has been attached. Following a wash, the RNA of interest is eluted by the addition of imidazole to the column, activating a mutant HdeltaV ribozyme incorporated into the tag. The affinity column can then be rapidly regenerated using conditions that release the protein-RNA tag interaction without denaturing the protein. To demonstrate that this method rapidly generates high-quality RNA, we have transcribed, purified, and generated diffraction-quality crystals of a mutant form of the Tetrahymena thermophila P4-P6 domain in a 48-h time period.

Affinity Labels↗
PubMed1994

Nucleolar introns from Physarum flavicomum contain insertion elements that may explain how mobile group I introns gained their open reading frames.

Comparison of two group I intron sequences in the nucleolar genome of the myxomycete Physarum flavicomum to their homologs in the closely related Physarum polycephalum revealed insertion-like elements. One of the insertion-like elements consists of two repetitive sequence motifs of 11 and 101 bp in five and three copies, respectively. The smaller motif, which flanks the larger, resembles a target duplication and indicates a relationship to transposons or retroelements. The insertion-like elements are found in the peripheral loops of the RNA structure; the positions occupied by the ORFs of mobile nucleolar group I introns. The P. flavicomum introns are 1184 and 637 bp in size, located in the large subunit ribosomal RNA gene, and can be folded into group I intron structures at the RNA level. However, the intron 2s from both P. flavicomum and P. polycephalum contain an unusual core region that lacks the P8 segment. None of the introns are able to self-splice in vitro. Southern analysis of different isolates indicates that the introns are not optional in myxomycetes.

Animals↗
PubMed2000

Use of terminal transferase-dependent antisense RNA amplification to determine the transcription start site of the Snrpn gene in individual neurons.

We describe here a very sensitive technique for RNA structure analysis and the determination of transcription start sites and demonstrate its use for mapping the start site of the imprinted Snrpn gene in individual hippocampal neurons. The method is adapted from reverse transcription-terminal transferase-dependent PCR (RT-TDPCR) to include amplification of the antisense sequence by in vitro transcription just prior to the final PCR step. The method should be useful for analysis of all genes for which variation in promoter usage and/or differences in RNA secondary structure may be specific to a given cell type or developmental stage.

Animals↗
PubMed1992

Novel GACG-hairpin pair motif in the 5' untranslated region of type C retroviruses related to murine leukemia virus.

We searched for the presence of common RNA structural motifs in mammalian type C retroviruses related to murine leukemia viruses and the closely related avian spleen necrosis virus. A novel motif consisting of a pair of hairpins, called hairpin pair motif, was detected in the 5' untranslated regions of the genomes of these retroviruses. A combination of computational analyses that included the assessment of phylogenetic sequence conservation by multiple alignment, the search for regions with unusual RNA folding properties, and the analysis of RNA secondary structure by suboptimal free-energy calculations highlighted the significance of this hairpin pair motif. The hairpin pair motif encompasses 70 to 80 nucleotides between the splice donor site and the gag translational initiation codon of these viruses. The motif is composed of two adjacent hairpins both with a perfectly conserved GACG tetraloop. We propose that the novel GACG-hairpin pair motif described here constitutes an essential component of the regulatory machinery in these type C retroviruses.

Base Sequence↗
PubMed2005

Programmed ribosomal frameshifting in decoding the SARS-CoV genome.

Programmed ribosomal frameshifting is an essential mechanism used for the expression of orf1b in coronaviruses. Comparative analysis of the frameshift region reveals a universal shift site U_UUA_AAC, followed by a predicted downstream RNA structure in the form of either a pseudoknot or kissing stem loops. Frameshifting in SARS-CoV has been characterized in cultured mammalian cells using a dual luciferase reporter system and mass spectrometry. Mutagenic analysis of the SARS-CoV shift site and mass spectrometry of an affinity tagged frameshift product confirmed tandem tRNA slippage on the sequence U_UUA_AAC. Analysis of the downstream pseudoknot stimulator of frameshifting in SARS-CoV shows that a proposed RNA secondary structure in loop II and two unpaired nucleotides at the stem I-stem II junction in SARS-CoV are important for frameshift stimulation. These results demonstrate key sequences required for efficient frameshifting, and the utility of mass spectrometry to study ribosomal frameshifting.

Base Sequence↗