Distribution of single sequence z scores for 5S rRNA, tRNA, and negative sequences. Distributions of RNAstructure-predicted z scores computed on the basis of folding single sequences for 5S rRNA and negatives generated from them (left figure) and tRNA and negatives generated from them (right figure). Real ncRNA are white, negatives are black. Controls were generated by the Altschul-Erikson dinucleotide shuffle of original sequence, with 100 controls for each test set sequence. 309 5S rRNA sequences and 482 tRNA sequences, plus one negative sequence generated from each real sequence by the Altschul-Erikson shuffle, were used for the test set.