New Tricks for Animal MicroRNAs: Targeting of Amino Acid Coding Regions at Conserved and Nonconserved Sites

MicroRNAs (miRNA) are short RNAs that affect the expression of a protein-coding gene either by directing the degradation of its "target" mRNA or by disrupting its translation into amino acids. Target selection depends on the underlying sequence as well as other, currently not understood, factors. In plants, miRNAs typically interact with the amino acid coding region of the target mRNA. However, in animals, research has been nearly exclusively confined to studying miRNA interactions with the 3' untranslated region of their mRNA targets. This region-limited view of animal miRNA activity, together with the assumption that bona fide animal miRNA targets ought to be conserved across organisms, have been in effect for many years. Recent work has shown that miRNAs can target extensively the amino acid coding region of animal mRNAs and can do so at locations that are not necessarily conserved across organisms.