A Horizontal Magnetic Tweezers For Studying Single Dna Molecules And Dna-Binding Proteins

We report data from single molecule studies on the interaction between single DNA molecules and core histones using custom-designed horizontal magnetic tweezers. The DNA-core histone complexes were formed using lambda-DNA tethers, core histones, and NAP1 and were exposed to forces ranging from similar to 2 pN to similar to 74 pN. During the assembly events, we observed the length of the DNA decrease in approximate integer multiples of similar to 50 nm, suggesting the binding of the histone octamers to the DNA tether. During the mechanically induced disassembly events, we observed disruption lengths in approximate integer multiples of similar to 50 nm, suggesting the unbinding of one or more octamers from the DNA tether. We also observed histone octamer unbinding events at forces as low as similar to 2 pN. Our horizontal magnetic tweezers yielded high-resolution, low-noise data on force-mediated DNA-core histone assembly and disassembly processes.