A number of super-unstable systems were obtained earlier by the induction of P-M hybrid dysgenesis in the strains with a mobilized Stalker. One of the super-unstable mutations appeared at the yellow locus of Drosophila melanogaster on the background of preexisting y mutation. The latter had been induced by mdg4 insertion into the regulatory region of the yellow locus. The suppressor genes of Hairy wing and modifier of mdg4 are known to encode proteins which bind to the mdg4 enhancer and are involved in the control of its transcription. A large spectrum of yellow alleles was obtained in super-unstable systems which could be recognized by the intensity of pigmentation in twelve different areas of the cuticle. Combining of these alleles with su(Hw) and mod(mdg4) mutations followed by the study of phenotype changes demonstrated that the same regulatory protein may influence expression of the gene in opposite directions.