Re-integration of sequence using the attP site present in TI{TI}CG4743KO (after first removing the loxP cassette), reconstituting a mutant CG4743 transcription unit at the native locus; contains a I172G amino acid substitution (this mutation is equivalent to a variant identified in the orthologous human SLC25A26 gene in a patient with severe mitochondrial disease). In addition, a loxP cassette containing a wGMR.PHb marker has been inserted downstream of the CG4743 coding sequence and the attP site has been converted into an attR site (this is located upstream of the CG4743 coding sequence).