Quantitative Analysis of the DNA Methylation Sensitivity of Transcription Factor Complexes

Although DNA modifications play an important role in gene regulation, the underlying mechanisms remain elusive. We developed EpiSELEX-seq to probe the sensitivity of transcription factor binding to DNA modification in vitro using massively parallel sequencing. Feature-based modeling quantifies the effect of cytosine methylation ((5)mC) on binding free energy in a position- specific manner. Application to the human bZIP proteins ATF4 and C/EBPb and three different Pbx-Hox complexes shows that 5 mCpG can both increase and decrease affinity, depending on where the modification occurs within the protein-DNAinterface. The TF paralogs tested vary in their methylation sensitivity, for which we provide a structural rationale. We show that 5 mCpG can also enhance in vitro p53 binding and provide evidence for increased in vivo p53 occupancy at methylated binding sites, correlating with primed enhancer histone marks. Our results establish a powerful strategy for dissecting the epigenomic modulation of protein-DNA interactions and their role in gene regulation.