Interallelic interaction and gene regulation in budding yeast.

InDrosophila, homologous chromosome pairing leads to "transvection," in which the enhancer of a gene can regulate the allelic transcription intrans.Interallelic interactions were also observed in vegetative diploid budding yeast, but their functional significance is unknown. Here, we show that aGAL1reporter can interact with its homologous allele and affect its expression. By ectopically inserting two allelic reporters, one driven by wild-typeGAL1promoter (WTGAL1pr) and the other by a mutant promoter with delayed response to galactose induction, we found that the two reporters physically associate, and the WTGAL1prtriggers 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 activated WTGAL1prtranscription. 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.