Phenotypic suppression of the Drosophila mitochondrial disease-like mutant tko super(25t) by duplication of the mutant gene in its natural chromosomal context

A mutation in the Drosophila gene technical knockout (tko super(25t)), encoding mitoribosomal protein S12, phenocopies human mitochondrial disease. We isolated three spontaneous X-dominant suppressors of tko super(25t) (designated Weeble), exhibiting almost wild-type phenotype and containing overlapping segmental duplications including the mutant allele, plus a second mitoribosomal protein gene, mRpL14. Ectopic, expressed copies of tko super(25t) and mRpL14 conferred no phenotypic suppression. When placed over a null allele of tko, Weeble retained the mutant phenotype, even in the presence of additional transgenic copies of tko super(25t). Increased mutant gene dosage can thus compensate the mutant phenotype, but only when located in its normal chromosomal context.