An approximately 868bp fragment from the t locus (the male specific element, 'MLE', the region between the Gr8a and CG1537 genes that are upstream of t), in which a block of approximately 80bp has been mutated such that every other nucleotide has been altered by a non-complementary nucleotide transversion, is fused upstream of a minimal Hsp70 promoter and the coding sequence for EGFP tagged with Tag:NLS(Unk).