Altering the position of arginine in the hydrophobic core or adding a second arginine is detrimental to dystrophin production The repositioning of an arginine from a flanking region into the core was unexpectedly well-tolerated (Pip6e-PMO) Two further Pip6-PMO conjugates were thus synthesized (Figure 1a) as derivatives of Pip6e-PMO. Pip6g-PMO contained a second arginine residue, which was moved from the second flanking region into the central hydrophobic core, and Pip6h-PMO contains an inversion of the Pip6e hydrophobic region, such that the single arginine location is altered within the core. (e) Representative western blot images for each treatment. Ten micrograms of total protein was loaded (TA, quadriceps, gastrocnemius, diaphragm, heart, and abdomen muscles) relative to 50% (5 µg protein) and 10% (1 µg) C57BL10 controls, and normalized to α-actinin loading control (for quantification see Supplementary Figure S2a) . PMO, phosphorodiamidate morpholino oligonucleotide.