A Magnetic Tweezers-Based Study of DNA-Histone Interactions

We report data from single-molecule forcemediated DNAcore histone assembly and disassembly processes using horizontal magnetic tweezers. The tweezers can apply stresses ranging from 0.01 to 100 pN and generate highresolution, low-noise data. DNA tethers, core histones, and NAP1 were used to create DNAcore histone complexes that were subjected to forces ranging from 2 pN to 80 pN. We noticed that the length of the DNA decreased in approximate integer multiples of 50 nm during the assembly process, suggesting histone octamers were bound to the DNA tether. We also found disruption lengths distributed around near integer multiples of 50 nm during mechanically induced disassembly events, again suggesting the unbinding of one or more octamers from the DNA tether. We also observed histone octamer unbinding events at forces as low as ~2 pN. Further, we present preliminary data from studies comparing the mechanical stability of native and post-translationally modified histones bound to DNA, which will help to quantify the relative affinities of histoneDNA interactions in nucleosomes.