Fig. 1.

Position-specific sequence and structural features for the target sites. Nucleotides at positions 2–8 (highlighted with a shaded box) in the target site are the miRNA seed-binding region. Statistical significance for each nucleotide position was calculated by comparing the target sites with non-target sites for base usage or accessibility. (A) Differences in base usage at individual positions between the target site and non-target site. P-values were calculated with χ² test. (B) Differences in structural accessibility at individual positions between the target site and non-target site. Local secondary structure was calculated with RNAfold, and the fractions of unstructured bases at individual positions of the target and non-target sites were compared with Student’s t-test