Multi-objective pairwise RNA sequence alignment

With an increase in the number of known biological functions of non-coding RNAs, the importance of RNA sequence alignment has risen. RNA sequence alignment problem has been investigated by many researchers as a mono-objective optimization problem where contributions from sequence similarity and secondary structure are taken into account through a single objective function. Since there is a trade-off between these two objective functions, usually we cannot obtain a single solution that has both the best sequence similarity score and the best structure score simultaneously. Multi-objective optimization is a widely used framework for the optimization problems with conflicting objective functions. So far, no one has examined how good alignments we can obtain by applying multi-objective optimization to structural RNA sequence alignment problem.

We developed a pairwise RNA sequence alignment program, Cofolga2mo, based on multi-objective genetic algorithm (MOGA). We tested Cofolga2mo with a benchmark dataset which includes sequence pairs with a wide range of sequence identity, and we obtained at most 100 alignments for each inputted RNA sequence pair as an approximate set of weak Pareto optimal solutions. We found that the alignments in the approximate set give benchmark results comparable to those obtained by the state-of-the-art mono-objective RNA alignment algorithms. Moreover, we found that our algorithm is efficient in both time and memory usage compared to the other methods.

Our MOGA programs for structural RNA sequence alignment can be downloaded at http://rna.eit.hirosaki-u.ac.jp/cofolga2mo/.