Advances in phase plate cryo-EM imaging of DNA and nucleosomes.

Contrast in electron cryo-microscopy (cryo-EM) is limited by the weak phase and radiation sensitive nature of biologic samples embedded in vitrified ice. We have recently shown that a new contrast enhancement technique utilizing the Volta phase plate can be combined with single particle analysis to determine the structure of a small chromatin complex, the nucleosome core particle, at near-atomic resolution. Here, we discuss advantages and limitations of the technique in terms of data collection, particle detection, and visualization of individual DNA molecules and higher-order chromatin structure.