Three-dimensional comparative modeling of RNA.

Comparative sequence analysis and ERNA-3D software were used to model the three-dimensional structure of the small domain of signal recognition particle RNA. RNA secondary structures were established by allowing only phylogenetically-supported base pairs. The folding of the RNA molecules was constrained further to include a well-supported pseudoknot. Helical sections were oriented coaxially where a continuous helical stack was formed in the RNA of another species. Finally, RNA helices were placed at distances that preserved the connectivity of the molecule with the smallest number of single-stranded nucleotide residues as identified from the aligned sequences. We show that the comparative three-dimensional structure modeling approach is an extremely powerful tool as it requires only a critical number of carefully aligned sequences.