Analysis of the accessibility of CLIP bound sites reveals that nucleation of the miRNA:mRNA pairing occurs preferentially at the 3′-end of the seed match

Dependence of the discrimination between bound and unbound sites on the location of the nucleation region within the seed match. (A) Numbering of the positions in the binding site. It is based on the corresponding numbering of positions in the miRNA. (B–G) Discrimination obtained when the nucleation region within the binding site is restricted to the positions indicated on the x-axis. For each length n, all possible locations were explored, always using the P_cutoff value indicated in Table 1. Statistical significance was evaluated with the unpaired one-sided t-test.