Nucleosome Dynamics Studied By Forster Resonance Energy Transfer

Chromatin is a hierarchical structure that condenses the genetic material into a nucleus of less than 10 mu m in diameter, while at the same time providing rapid on-demand access to specific DNA loci. This dual role requires a tightly regulated yet highly dynamic DNA packaging, with the nucleosome as the central repeating unit. The nucleosome is composed of multiple protein subunits with distinct dynamic properties and can undergo spontaneous conformational transitions. Forster Resonance Energy Transfer (FRET) is a powerful method to analyze such conformational changes in nucleosomes. In this chapter we will review its concepts and describe different implementations of FRET, with a special emphasis on single molecule techniques. We will conclude with a brief overview of recent experiments, where FRET was successfully used to shed light on the dynamic properties of nucleosomes. These include the unwrapping dynamics in the entry/exit region, the pathway by which they disassemble and the role of posttranslational modifications on nucleosome architecture.