What are small RNAs?

Small noncoding RNA molecules (20-30 nt). Found in all eukaryotes (except yeast). >60% of human protein-coding genes contain at least one conserved miRNA-binding site, plus other most protein-coding genes may be under the control of miRNAs. 3 Different key types of small RNA: miRNA (22nt, transaltional repression and mRNA degradation), siRNA (21nt, RNA cleavage) and piRNA (24-30nt, transcriptional repression of transposons)