The oxen gene of drosophila encodes a homolog of subunit 9 of yeast ubiquinol-cytochrome c oxidoreductase complex: Evidence for modulation of gene expression in response to mitochondrial activity

A P-element insertion in the oxen gene, ox(1), has been isolated in a searc h for modifiers of white gene expression. The mutation preferentially exert s a negative dosage effect upon time expression of three genes encoding ABC : transporters involved in pigment precursor transport, white, brown, and s carlet. A precise excision of the P element reverts time mutant phenotype. Five different transcription units were identified around time insertion si te. To distinguish a transcript responsible for the mutant phenotype, a set of deletions within the oxen region was generated. Analysis of gene expres sion within the oxen region in the case of deletions as well as generation of transgenic flies allowed us to identify the transcript responsible for o xen function. It encodes a 6.6-kD homolog of mitochondrial ubiquinol cytoch rome c oxidoreductase (QCR9), subunit. 9 of the bc(1) complex in yeast. In addition to white, brown, and scarlet, oxen regulates the expression of thr ee of seven tested genes. Tl-ius, our data provide additional evidence for a cellular response to changes in mitochondrial function. The oxen mutation provides a model for the genetic analysis in multicellular organisms of th e effect of mitochondrial activity on nuclear gene expression.