The 5' leaders of many uORF-containing ARF mRNAs render translation dependent on eIF3h. (A) Schematic view of the mRNAs for protoplast transformation. Open arrows represent RLUC ORF, hatched arrows represent codon-optimized FLUC (LUC+). mRNAs were prepared by in vitro transcription with SP6 RNA polymerase. An equal amount of internal control (Spacer-LUC+) mRNA was added to the 5' leader-RLUC mRNA to be tested as an internal control for transformation efficiency. (B and C) Translational efficiency on the given ARF 5' leader is expressed as the mean RLUC/FLUC ratio with standard errors from three replicate transformations. Data from several other auxin related 5' leaders are shown for comparison. PIN1 does not contain uORFs. AUX1 and TIR1 each have one short uORF of six codons.