Under low salt concentrations, histones are visible as ‘beads on a string’, in the 10 nm fibre (a less condensed structure than is observed under physiological conditions). At physiological salt concentrations, the 30 nm fibre is observed. This is a thicker, more condensed DNA-nucleosome complex, and is less transcriptionally active. Although the precise structure of the 30 nm fibre is not fully known, the two dominant theories are ellipsoid (a coiled structure) and zig-zag (2 helices with nucleosomes passing between them).
By being able to demonstrate cDNA is able to dynamically transition between these two states (the 10 nm and 30 nm fibre), it is possible to transition between transcriptionally active and inactive conformations. As histone proteins are not attached to the DNA, but instead can move along them, the 10 nm fibre is therefore more transcriptionally active, as the polymerase is able to slide histones along the DNA, enabling gene expression (with an RNA polymerase) and DNA synthesis (with a DNA polymerase).