Transcription Factor Condensates Mediate Clustering of MET Regulon and Enhancement in Gene Expression [MeDIP]
Some transcription factors (TFs) can form liquid-liquid phase separated (LLPS) condensates. However, the function of these TF condensates in 3D genome organization and gene regulation remains elusive. In response to methionine (met) starvation in budding yeast, Met4 and a few sequence-specific co-activators, including Met32, induce a set of genes involved in met biosynthesis. Here, we show that the endogenous Met4 and Met32 form puncta-like structures that significantly overlap in yeast nuclei upon met depletion. Recombinant Met4 and Met32 form mixed droplets with LLPS properties in vitro. In relation to chromatin, Met4 puncta co-localize with target genes, and at least a subset of these target genes are clustered in 3D in a Met4-dependent manner. A MET3pr-GFP reporter inserted near several native Met4 binding sites becomes co-localized with Met4 puncta and displays enhanced transcriptional activity. A Met4 variant with a partial truncation of an intrinsically disordered region (IDR) shows less puncta formation, and this mutant selectively reduces the reporter activity near Met4 binding sites to the basal level. Overall, these results support a model where Met4 and co-activators form condensates to bring multiple target genes into a vicinity with higher local TF concentrations, which facilitates a strong response to met depletion (-met). Overall design: MeDip of MTAC strains with MET13, MET6 as VP in MET active (-met) and inactive (+met) conditions with +/- IAA for Met4 depletion.