Peter De Rijk

Database on the Structure of Large Ribosomal Subunit RNA

About 8600 complete or nearly complete sequences are now available from the Antwerp database on small ribosomal subunit RNA. All these sequences are aligned with one another on the basis of the adopted secondary structure model, which is corroborated by the observation of compensating substitutions in the alignment. Literature references, accession numbers and detailed taxonomic information are also compiled. The database can be consulted via the World Wide Web at URL http://rrna.uia.ac.be/ssu/

Compilation of small ribosomal subunit RNA structures

The database on small ribosomal subunit RNA structure contained 1804 nucleotide sequences on April 23, 1993. This number comprises 365 eukaryotic, 65 archaeal, 1260 bacterial, 30 plastidial, and 84 mitochondrial sequences. These are stored in the form of an alignment in order to facilitate the use of the database as input for comparative studies on higher-order structure and for reconstruction of phylogenetic trees. The elements of the postulated secondary structure for each molecule are indicated by special symbols. The database is available on-line directly from the authors by ftp and can also be obtained from the EMBL nucleotide sequence library by electronic mail, ftp, and on CD ROM disk.

DCSE, an interactive tool for sequence alignment and secondary structure research.

DCSE provides a user-friendly package for the creation and editing of sequence alignments. The program runs on different platforms, including microcomputers and workstations. Apart from available hardware, the program is not limited in the size of the alignment it can handle. It deviates more from classical text editors than other available sequence editors because it uses a different approach towards editing. It shifts characters or entire blocks of aligned characters, rather than inserting or deleting gaps in the sequences. Alignment of a new sequence to an existing alignment is partly automated. Although DCSE can be used on protein sequence alignments, it is especially targeted at the examination of RNA. The secondary structure for every sequence can be incorporated easily in the alignment. DCSE also has extensive built-in support for finding and checking secondary structure elements. A sophisticated system of markers allows notation of special positions in an alignment. This system can be used to store information such as the position of hidden breaks, introns and tertiary structure interactions.

The European Large Subunit Ribosomal RNA database

The European Large Subunit (LSU) Ribosomal RNA (rRNA) database is accessible via the rRNA WWW Server at URL http://rrna.uia.ac.be/lsu/. It is a curated database that compiles complete or nearly complete LSU rRNA sequences in aligned form, and also incorporates secondary structure information for each sequence. Taxonomic information, literature references and other information about the sequences are also available, and can be searched via the WWW interface.

RnaViz 2: an improved representation of RNA secondary structure

SUMMARY RnaViz has been developed to easily create nice, publication quality drawings of RNA secondary structure. RnaViz 2 supports CT, DCSE, and RNAML input formats and improves on many aspects of the first version, notably portability and structure annotation. RnaViz is written using a hybrid programming approach combining pieces written in C and in the scripting language Tcl/Tk, making the program very portable and extensible. AVAILABILITY Source code, binaries for Linux and MS Windows, and additional documentation are available athttp://rrna.uia.ac.be/rnaviz/

The European Small Subunit Ribosomal RNA database

The European database of the Small Subunit (SSU) Ribosomal RNA is a curated database that strives to collect all information about the primary and secondary structure of completely or nearly-completely sequenced rRNAs. Furthermore, the database compiles additional information such as literature references and taxonomic status of the organism the sequence was derived from. The database can be consulted via the WWW at URL http://rrna.uia.ac.be/ssu/. Through the WWW, sequences can be easily selected either one by one, by taxonomic group, or by a combination of both, and can be retrieved in different sequence and alignment formats.

Database on the structure of large subunit ribosomal RNA

The Antwerp database on large subunit ribosomal RNA now contains 607 complete or nearly complete aligned sequences. The alignment incorporates secondary structure information for each sequence. Other information about the sequences, such as literature references, accession numbers and taxonomic information is also available. Information from the database can be downloaded or searched on the rRNA WWW Server at URL http://rrna.uia.ac.be/

Resequencing of positional candidates identifies low frequency IL23R coding variants protecting against inflammatory bowel disease

Genome-wide association studies (GWAS) have identified dozens of risk loci for many complex disorders, including Crohns disease. However, common disease-associated SNPs explain at most ∼20% of the genetic variance for Crohns disease. Several factors may account for this unexplained heritability, including rare risk variants not adequately tagged thus far in GWAS. That rare susceptibility variants indeed contribute to variation in multifactorial phenotypes has been demonstrated for colorectal cancer, plasma high-density lipoprotein cholesterol levels, blood pressure, type 1 diabetes, hypertriglyceridemia and, in the case of Crohns disease, for NOD2 (refs. 14,15). Here we describe the use of high-throughput resequencing of DNA pools to search for rare coding variants influencing susceptibility to Crohns disease in 63 GWAS-identified positional candidate genes. We identify low frequency coding variants conferring protection against inflammatory bowel disease in IL23R, but we conclude that rare coding variants in positional candidates do not make a large contribution to inherited predisposition to Crohns disease.

Reconstructing evolution from eukaryotic small-ribosomal-subunit RNA sequences: Calibration of the molecular clock

The detailed descriptions now available for the secondary structure of small-ribosomalsubunit RNA, including areas of higly variable primary structure, facilitate the alignment of nucleotide sequences. However, for optimal exploitation of the information contained in the alignment, a method must be available that takes into account the local sequence variability in the computation of evolutionary distance. A quantitative definition for the variability of an alignment position is proposed in this study. It is a parameter in an equation which expresses the probability that the alignment position contains a different nucleotide in two sequences, as a function of the distance separating these sequences, i.e., the number of substitutions per nucleotide that occurred during their divergence. This parameter can be estimated from the distance matrix resulting from the conversion of pairwise sequence dissimilarities into pairwise distances. Alignment positions can then be subdivided into a number of sets of matching variability, and the average variability of each set can be derived. Next, the conversion of dissimilarity into distance can be recalculated for each set of alignment positions separately, using a modified version of the equation that corrects for multiple substitutions and changing for each set the parameter that reflects its average variability. The distances computed for each set are finally averaged, giving a more precise distance estimation.Trees constructed by the algorithm based on variability calibration have a topology markedly different from that of trees constructed from the same alignments in the absence of calibration. This is illustrated by means of trees constructed from small-ribosomal-subunit RNA sequences of Metazoa. A reconstruction of vertebrate evolution based on calibrated alignments matches the consensus view of paleontologists, contrary to trees based on uncalibrated alignments. In trees derived from sequences covering several metazoan phyla, artefacts in topology that are probably due to a high clock rate in certain lineages are avoided.

Evolution According to Large Ribosomal Subunit RNA

Evolutionary trees were constructed, by distance methods, from an alignment of 225 complete large subunit (LSU) rRNA sequences, representing Eucarya, Archaea, Bacteria, plastids, and mitochondria. A comparison was made with trees based on sets of small subunit (SSU) rRNA sequences. Trees constructed on the set of 172 species and organelles for which the sequences of both molecules are known had a very similar topology, at least with respect to the divergence order of large taxa such as the eukaryotic kingdoms and the bacterial divisions. However, since there are more than ten times as many SSU as LSU rRNA sequences, it is possible to select many SSU rRNA sequence sets of equivalent size but different species composition. The topologies of these trees showed considerable differences according to the particular species set selected.The effect of the dataset and of different distance correction methods on tree topology was tested for both LSU and SSU rRNA by repetitive random sampling of a single species from each large taxon. The impact of the species set on the topology of the resulting consensus trees is much lower using LSU than using SSU rRNA. This might imply that LSU rRNA is a better molecule for studying wide-range relationships. The mitochondria behave clearly as a monophyletic group, clustering with the Proteobacteria. Gram-positive bacteria appear as two distinct groups, which are found clustered together in very few cases. Archaea behave as if monophyletic in most cases, but with a low confidence.