Small changes in free energy assignments for unpaired bases do not affect predicted secondary structures in single stranded RNA.

We present extensive calculations of the secondary structure of mRNA which point to its insensitivity to small changes in the free energy assignments of single stranded regions. Truncating the free energies of hairpin loops, bulges, internal loops and multibranched junctions to two significant digits yields structures nearly identical to those generated using three digit values. The results show that one can safely use truncated values in RNA folding calculations. The implementation of these results enabled us to carry out secondary structure calculations on 2600 nucleotides in a single computer run.