RNA silencing is a conserved regulatory mechanism in fungi, plants and animals that regulates gene expression and defence against viruses and transgenes. A conserved S-adenosyl-l-methionine-dependent RNA methyltransferase, HUA ENHANCER 1 (HEN1), and its homologues are responsible for 2'-O-methylation on the 3' terminal nucleotide of microRNAs and small interfering RNAs (siRNAs). The 2'-O-methylation protects miRNAs and siRNAs from 3'-end uridylation and 3'-to-5' exonuclease-mediated degradation. This domain lies on the C-terminal region of the La-motif domain found in HEN1 [1].

1: Structural insights into mechanisms of the small RNA methyltransferase HEN1. Huang Y, Ji L, Huang Q, Vassylyev DG, Chen X, Ma JB; Nature. 2009;461:823-827. PMID:19812675