Dissection of molecular assembly dynamics by tracking orientation and position of single molecules in live cells

Regulation of order, such as orientation and conformation, drives the function of most molecular assemblies in living cells, yet remains difficult to measure accurately through space and time. We built an instantaneous fluorescence polarization microscope, which simultaneously images position and orientation of fluorophores in living cells with single-molecule sensitivity and a time resolution of 100ms. We developed image acquisition and analysis methods to track single particles that interact with higher-order assemblies of molecules. We tracked the fluctuations in position and orientation of molecules from the level of an ensemble of fluorophores down to single fluorophores. We tested our