Supercoiling-mediated feedback rapidly couples and tunes transcription

Transcription induces a wave of DNA supercoiling, altering the binding affinity of RNA polymerases and reshaping the biochemical landscape of gene regulation. As supercoiling rapidly diffuses, transcription dynamically reshapes the regulation of proximal genes, forming a complex feedback loop. The resulting intergene coupling may provide a mechanism to control transcriptional variance in engineered gene networks and explain the behavior of co-localized native circuits. However, a theoretical framework is needed for integrating both biophysical and biochemical transcriptional regulation to investigate the role of supercoiling-mediated feedback within multi-gene systems. Here, we model transcriptional regulation under the influence of supercoiling-mediated polymerase dynamics, allowing us to identify patterns of expression that result from physical intergene coupling and explore integration of this biophysical model with a set of canonical biochemical gene regulatory systems. We find that gene syntax--the relative ordering and orientation of genes--defines the expression profiles, variance, burst dynamics, and intergene correlation of two-gene systems. By applying our model to both a synthetic toggle switch and the endogenous zebrafish segmentation network, we find that supercoiling can enhance or weaken conventional biochemical regulatory strategies such as mRNA- and protein-mediated feedback loops. Together, our results suggest that supercoiling couples behavior between neighboring genes, representing a novel regulatory mechanism. Integrating biophysical regulation into the analysis and design of gene regulation provides a framework for enhanced understanding of native networks and engineering of synthetic gene circuits.