3′ Terminal oligo U-tract-mediated stimulation of decapping

Abstract

Decapping is a critical step in the control of gene expression and is regulated by both positive and negativetransfactors. Less is known aboutciselements that promote decapping. In plants, following microRNA (miRNA)-directed cleavage of an mRNA, a uridine tract can be added onto the exposed 3′ end of the resulting 5′ fragment, which can promote 5′ end decay. We now demonstrate that in mammalian cell extract, addition of five uridine residues to the 3′ end of an RNA (U₅) promotes decapping relative to an RNA lacking the uridines (U₀). Although the decapping stimulation observed in extract required hDcp2, recombinant hDcp2 was unable to support differential decapping of the U₀and U₅RNAs, indicating that the stimulation was likely due to an indirect recruitment of hDcp2 to the RNA. Consistent with the promotion of 5′ end decapping by the uridine tract, affinity purification with the U₅RNA revealed the presence of a decapping subcomplex at least consisting of hDcp2, Dcp1a, Edc4, LSm1, and LSm4 that were specifically bound to the U₅RNA but not the U₀RNA. In addition to promoting decapping, the U-tract stabilized the 3′ end of the RNA by preventing 3′ to 5′ exonucleolytic decay to ensure 5′ end directional degradation. These data suggest that following post-transcriptional oligo uridylation of an mRNA or mRNA fragment, the U-tract has the capacity to specifically stimulate 5′ end decapping to expedite mRNA decay.