The function of the Drosophila thioredoxin homologue encoded by the deadhead gene is redox-dependent and blocks the initiation of development but not DNA synthesis

Thioredoxin is a highly conserved disulfide reducing protein whose structure and biochemical properties have been extensively studied. Nonetheless, its function in vivo is not well defined. In Drosophila, the maternal-effect gene deadhead encodes a thioredoxin-like protein that is required for initiation of embryonic development. Here we report that deadhead function is dependent on its enzymatic activity: transgenes carrying mutations in thioredoxin's conserved active site failed to rescue the deadhead mutant phenotype. A number of studies have documented that thioredoxin plays a role in DNA synthesis. If thioredoxin is required for DNA synthesis in the fly, then deadhead mutations will suppress mutations that inappropriately synthesize DNA. Contrary to expectation, we find that deadhead does not function as a suppressor in this assay. The observed epistatic relationship between these mutations clearly indicates that deadhead is not essential for DNA metabolism. The possibility of a regulatory role in controlling the initiation of S-phase is discussed.