We regard GU base pair fraction rather of the consensus structure than of the predicted structures of the single sequences, as the structure prediction of RNAalifold is based on evolutionary information of a set of sequences and hence produces a fold more similar to the real structure than RNAfold is able to predict from one single sequence. We did not introduce the difference of GU base pairs as a descriptor, because the error rate of such an descriptor depends largely on the correctness of the predicted secondary structure. Small errors in structure prediction have a large impact on the difference of GU base pairs. In contrast, the difference in structure stability and conservation regards all base pairs and hence depends only very weakly on the correctness of individual base pairs.