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: virtually every nucleotide in the evolutionary conserved exon 2 sequence is mutated while changing the intron 0 sequence pairing with this region by introducing compensatory base changes, thereby retaining a secondary structure identical to wild type.