Andy Quaen Chen Rose Hills
Observing Histone Loss in Individual Nucleosomes through Mechanical Unwrapping
I will investigate how histones dissociate from the nucleosome during the process of unwrapping by using “Fleezers,” optical tweezers with the added capability of detecting single molecule fluorescence. In all Eukaryotic cells, DNA is packaged and compacted in the form of chromatin in the nucleus. The nucleosome, consisting of a histone octamer core wrapped by 1.7 turns of the DNA, represents the basic, repeating, unit of chromatin. Since the DNA is constantly transcribed, repressed, repaired or replicated in response to stimuli, nucleosomes and the superstructures they form must be highly dynamic and amenable to modification by chromatin remodelers, chaperones, and histone-modifying enzymes. During some of these processes, DNA unwrapping from the nucleosome core can cause histones to dissociate, producing hexasomes and tetrasomes. In order to study the process of histone disassociation, we will use optical tweezers to exert force on the DNA ends of individual nucleosomes and unwrap the DNA from the octamer. By using fluorescently labeled histones, we can observe the real-time loss of the histone dimer during the unwrapping process. This will help us understand the behavior of this fundamental unit of chromatin when it is unwrapped under force, such as during the passage of polymerases or under remodeling activity by molecular motors.