Nature - Primary transcripts of microRNAs encode regulatory peptides

MicroRNAs are small RNAs (approximately 21 nucleotides) that control most biological processes, negatively regulating the expression of many target genes. They are present in plants and animals, inclu- ding humans, in which they are involved in many diseases when their expression is dere- gulated. MicroRNAs are derived from primary transcripts, which are larger RNA molecules produced by transcription of the DNA. Prima- ry transcripts of microRNAs have long been regarded as non-coding RNAs.