Experimentally identified miRNA-mRNA interactions. (a) A method was recently developed to sequence miRNAs ligated to their mRNA targets . In these data, we identified 256 distinct interactions between 87 novel miRNAs and 245 mRNAs. The inferred binding energies of the novel miRNAs are similar to those of known miRNAs, and are significantly stronger than the binding of shuffled control sequences (P <0.001, sub-sampling). (b) The miRNA-mRNA interactions were grouped based on 5' seed pairing. Both novel and known miRNAs tend to bind by canonical seed pairing, in contrast with control sequences. nt, nucleotide.