Ubi-p63E promoter and 5'UTR sequences are fused upstream of EGFP. The codon usage of the EGFP coding sequence has been modified (by synonymous codon substitutions) so that 50% of the codons correspond to the most rarely used synonymous codon in the D. melanogaster genome. The rare synonymous codons are dispersed throughout the EGFP sequence and the remaining codons are split between the most commonly used synonymous codon in the D. melanogaster genome and 'middle' codons (synonymous codon(s) with a usage frequency in between the rare and most commonly used ones).