In Drosophila, homologous chromosome pairing leads to "transvection," in which the enhancer of a gene can regulate the allelic transcription in trans. Interallelic interactions were also observed in vegetative diploid budding yeast, but their functional significance is unknown. Here, we show that a GAL1 reporter can interact with its homologous allele and affect its expression. By ectopically inserting two allelic reporters, one driven by wild-type GAL1 promoter (WT GAL1pr) and the other by a mutant promoter with delayed response to galactose induction, we found that the two reporters physically associate, and the WT GAL1pr triggers synchronized firing of the defective promoter and accelerates its activation without affecting its steady-state expression level. This interaction and the transregulatory effect disappear when the same reporters are located at nonallelic sites. We further demonstrated that the activator Gal4 is essential for the interallelic interaction, and the transregulation requires fully activatedWT GAL1pr transcription. The mechanism of this phenomenon was further discussed. Taken together, our data revealed the existence of interallelic gene regulation in yeast, which serves as a starting point for understanding long-distance gene regulation in this genetically tractable system.
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