Revealing chromatin dynamics on the single-molecule scale

The elucidation of the structure and dynamics of chromatin, the nucleoprotein complex organizing the eukaryotic genome, is a problem spanning orders of magnitude in spatial (Å to micrometers) and temporal (microseconds to hours) scales. Chromatin structure and dynamics control access to the genomic DNA, thereby forming a critical gate for gene regulation. These processes are tightly controlled by effector proteins that bind to combinations of chemical modifications on the chromatin surface. The dynamic architecture of chromatin is currently still poorly understood, due to a lack of methods suitable to study large heterogeneous complexes.

We combine chemical chromatin synthesis and single-molecule imaging to study how multivalent effector proteins dynamically interact with modified chromatin and control chromatin structure and dynamics. Our approaches allowed us dissect the dynamics of key protein factors in gene silencing. Conversely, using a multimodal single-molecule Förster resonance energy transfer (smFRET) approach we revealed the structural states and their interconversion kinetics in chromatin fibers. Chromatin thus samples a complex energy landscape modulated by chemical modifications and interacting proteins, controlling gene function.