5X UAS regulates expression of EGFP. A mutated 177nt 5'UTR (comprising intron 0 and part of exon 2) of Rnp4F, that potentially folds into a single long stable stem loop, is inserted between the UAS and the EGFP sequences: the evolutionary conserved exon 2 sequence is retained, but other nucleotides within intron 0 are changed to completely disrupt the wild type secondary structure.