Heterodimeric transcription factors are ubiquitous in eukaryotes. In cases such as that of the bHLHZ, bZIP, and type II nuclear receptors, such proteins associate into complex regulatory networks that have been difficult to dissect with in vitro biochemistry. Two new technologies – efficient endogenous gene tagging and single-molecule microscopy – enable us to begin interrogating the biochemistry of these networks in their native context.
In my project, I leverage recent advances in gene editing and single-molecule localization microscopy to quantify the concentration and binding kinetics of type II nuclear receptors (T2NRs) in live cells. This system represent an extreme case of competition in which over 10 distinct T2NRs compete for the same class of heterodimeric partners, the retinoid X receptors (RXRs). Understanding the nature of competitive effects in this system may help us to understand diseases in which the concentration or oligomeric state of T2NRs is altered. More generally, it may help us to understand the critical parameters in systems comprised of hierarchical protein-protein and protein-DNA interactions.