A synthetic 8-mer, amphipathic, trans-acting poly-2'-O-methyluridylic thiophosphate triester RNA element (2'-OMeUtaPS) can be prepared using solid-phase synthesis protocols. 2'-OMeUtaPS efficiently mediates the delivery of uncharged polyA-tailed phosphorodiamidate morpholino (PMO) sequences in HeLa pLuc 705 cells, as evidenced by flow cytometry measurements. In this cell line, 2'-OMeUtaPS-mediated transfection of an antisense polyA-tailed PMO sequence induces alternative splicing of an aberrant luciferase pre-mRNA splice site, leading to restoration of functional luciferase, as quantitatively measured using a typical luciferase assay. 2'-OMeUtaPS is also potent at delivering an uncharged antisense polyA-tailed PMO sequence in muscle cells of the mdx mouse model of muscular dystrophy; targeting the polyA-tailed PMO sequence against a splice site of the pre-mRNA encoding mutated dystrophin triggers an alternate splicing event that results in excision of the mutated exon (exon 23) from the pre-mRNA and production of functional dystrophin, as demonstrated by agarose gel electrophoresis. © 2018 by John Wiley & Sons, Inc.