Integrated requirement of non-specific and sequence-specific DNA binding in MYC-driven transcription

Eukaryotic transcription factors recognize specific DNA sequence motifs, but are also endowed with generic, non-specific DNA-binding activity: how these binding modes are integrated to determine select transcriptional outputs remains unresolved. We designed mutants of the MYC transcription factor bearing substitutions in residues that contact either the DNA backbone or specific bases within the consensus binding motif (E-box), and profiled their DNA-binding and gene-regulatory activities in murine cells. Our data reveal that non-specific DNA binding is required for MYC to engage onto active regulatory elements in the genome, preceding sequence recognition; beyond merely stabilizing MYC onto select target loci, sequence-specific binding contributes to its precise positioning and - most unexpectedly - to transcriptional activation per se. In particular, at any given binding intensity, promoters targeted via the cognate DNA motif were more frequently activated by MYC. Hence, seemingly promiscuous chromatin interaction profiles actually encompass diverse DNA-binding modalities, driving defined, sequence-dependent transcriptional responses.