Fig. 3

The unpaired nucleotide frequency (UNF) across the miRNA sequence. 5′ end of the miRNA starts from position one. Negative positions correspond to the miRNA flank. The UNF is not shown at the very ends of several long miRNAs. a Animal miRNAs. b The UNF dependence on the relative rate of nucleotide substitutions in animal miRNAs [62]. The seed points concentrate near the very UNF-axis. Spearman’s rank correlation test was used to estimate the significance of the correlation between the UNF and the rate of nucleotide substitutions (ρ = 0.81, P = 2.76 × 10^− 6). c-d The UNF profile of 5′ miRNAs and of 3′ miRNAs of human and mouse (mirtrons and non-mirtrons) and of animal excluding human and mouse