Some miRNAs in plants have been seen to contain 2'-O-methylation, a modification to the ribose sugar that is added by the methyltransferase HEN1. This modification is thought to protect the miRNA against polyuridylation, which would result in its subsequent degradation.
In addition, pri-miRNAs have been shown to contain mA. This reversible modification may affect their cellular localization and function during miRNA processing.