Human cytosolic tRNase Z can downregulate gene expression through miRNA

A long form of tRNase Z (tRNase Z^L) can cleave any target RNA at any desired site under the direction of artificial small guide RNA including ∼25-nucleotide hook-shaped RNA. Here we show that human miR-103 can form a hook structure to guide target RNA cleavage by human cytosolic tRNase Z^L in vitro. In vivo analyses using luciferase mRNAs modified to contain miR-103 target sequences in their 3′ untranslated regions indicated that miR-103 downregulates gene expression through directing mRNA cleavage by tRNase Z^L. The present data suggest the possibility that human cytosolic tRNase Z^L modulates gene expression through a subset of microRNAs in the cells.