  Metrics for indirectly predicting the folding rates of RNA sequences are of
interest. In this letter, we introduce a simple metric of RNA structural
complexity, which accounts for differences in the energetic contributions of
RNA base contacts toward RNA structure formation. We apply the metric to RNA
sequences whose folding rates were previously determined experimentally. We
find that the metric has good correlation (correlation coefficient: -0.95, p <<
0.01) with the logarithmically transformed folding rates of those RNA
sequences. This suggests that the metric can be useful for predicting RNA
folding rates. We use the metric to predict the folding rates of bacterial and
eukaryotic group II introns. Future applications of the metric (e.g., to
predict structural RNAs) could prove fruitful.
