Article

# Alignment of RNA base pairing probability matrices.

Institut für Theoretische Chemie und Molekulare Strukturbiologie, Universität Wien, Währingerstrasse 17, Vienna, Austria.

Bioinformatics (Impact Factor: 5.32). 10/2004; 20(14):2222-7. DOI: 10.1093/bioinformatics/bth229 Source: PubMed

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**ABSTRACT:**Incorporating secondary structure information into the alignment process improves the quality of RNA sequence alignments. Instead of using fixed weighting parameters, sequence and structure components can be treated as different objectives and optimized simultaneously. The result is not a single, but a Pareto-set of equally optimal solutions which all represent different possible weighting parameters. We now provide the interactive graphical software tool RNA-Pareto which allows a direct inspection of all feasible results to the pairwise RNA sequence-structure alignment problem and greatly facilitates the exploration of the optimal solution set.Availability and Implementation: The software is written in Java 6 (graphical user interface) and C++ (dynamic programming algorithms). The source code and binaries for Linux, Windows and Mac OS are freely available at http://sysbio.uni-ulm.de and are licensed under the GNU GPLv3. hans.kestler@uni-ulm.de.Bioinformatics 09/2013; · 5.47 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**BACKGROUND: The search for distant homologs has become an import issue in genome annotation. A particular difficulty is posed by divergent homologs that have lost recognizable sequence similarity. This same problem also arises in the recognition of novel members of large classes of RNAs such as snoRNAsor microRNAs that consist of families unrelated by common descent. Current homology search tools for structured RNAs are either based entirely on sequence similarity (such as blast or hmmer) or combine sequence and secondary structure. The most prominent example of the latter class of tools is Infernal. Alternatives are descriptor-based methods. In most practical applications published to-date, however, the information contained in covariance models or manually prescribed search patterns is dominated by sequence information. Here we ask two related questions: (1) Is secondary structure alone informative for homology search and the detection of novel members of RNA classes? (2) To what extent is the thermodynamic propensity of the target sequence to fold into the correct secondary structure helpful for this task? RESULTS: Sequence-structure alignment can be used as an alternative search strategy. In this scenario, the query consists of a base pairing probability matrix, which can be derived either from a single sequence or from a multiple alignment representing a set of known representatives. Sequence information can be optionally added to the query. The target sequence is pre-processed to obtain local base pairing probabilities. As a search engine we devised a semi-global scanning variant of LocARNA's algorithm for sequence-structure alignment. The LocARNAscan tool is optimized for speed and low memory consumption. In benchmarking experiments on artificial data we observe that the inclusion of thermodynamic stability is helpful, albeit only in a regime of extremely low sequence information in the query. We observe, furthermore, that the sensitivity is bounded in particular by the limited accuracy of the predicted local structures of the target sequence. CONCLUSIONS: Although we demonstrate that a purely structure-based homology search is feasible in principle, it is unlikely to outperform tools such as Infernal in most application scenarios, where a substantial amount of sequence information is typically available. The LocARNAscan approach will profit, however, from high throughput methods to determine RNA secondary structure. In transcriptomewide applications, such methods will provide accurate structure annotations on the target side. AVAILABILITY: Source code of the free software LocARNAscan 1.0 and supplementary data are available at http://www.bioinf.uni-leipzig.de/Software/LocARNAscan.Algorithms for Molecular Biology 04/2013; 8(1):14. · 1.61 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**MOTIVATION: The calculation of reliable alignments for structured RNA is still considered as an open problem. One approach is the incorporation of secondary structure information into the optimisation criteria by using a weighted sum of sequence and structure components as an objective function. Since it is not clear how to choose the weighting parameters, we use multi-objective optimisation to calculate a set of Pareto-optimal RNA sequence- structure alignments. The solutions in this set then represent all possible trade-offs between the different objectives, independent of any prior weighting. RESULTS: We present a practical multi-objective dynamic programming algorithm which is a new method for the calculation of the set of Pareto-optimal solutions to the pairwise RNA sequence-structure alignment problem. In selected examples, we show the usefulness of this approach, and its advantages over state-of-the-art single- objective algorithms. AVAILABILITY: The source code of our software (ISO C++11) is freely available at http://sysbio.uni-ulm.de/?Software and is licensed under the GNU GPLv3. CONTACT: hans.kestler@uni-ulm.de SUPPLEMENTARY INFORMATION: Suppelementary data are available at Bioinformatics online.Bioinformatics 04/2013; · 5.47 Impact Factor

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