Noncooperative Interactions between Transcription Factors and Clustered DNA Binding Sites Enable Graded Transcriptional Responses to Environmental Inputs

SummaryA paradigm in transcriptional regulation is that graded increases in transcription factor (TF) concentration are translated into on/off transcriptional responses by cooperative TF binding to adjacent sites. Digital transcriptional responses underlie the definition of anatomical boundaries during development. Here we show that NF-κB, a TF controlling inflammation and immunity, is conversely an analog transcriptional regulator that uses clustered binding sites noncooperatively. We observed that increasing concentrations of NF-κB are translated into gradual increments in gene transcription. We provide a thermodynamic interpretation of the experimental observations by combining quantitative measurements and a minimal physical model of an NF-κB-dependent promoter. We demonstrate that NF-κB binds independently to adjacent sites to promote additive RNA Pol II recruitment and graded transcriptional outputs. These findings reveal an alternative mode of operation of clustered TF binding sites, which might function in biological conditions where the transcriptional output is proportional to the strength of an environmental input.

Graphical AbstractFigure optionsDownload high-quality image (242 K)Download as PowerPoint slideHighlights
► Homotypic clusters of binding sites are found at genes regulated by environmental TFs
► Sites in clusters operate independently and regulate Pol II recruitment additively
► Lack of binding cooperativity generates analog rather than on/off (digital) responses
► Additive use of multiple sites expands the dynamic range of transcriptional activity