Localization of linker histone in chromatosomes by cryo-atomic force microscopy

Linker histones play a fundamental role in determining higher order chromatin structure as a consequence of their association with nucelosomal DNA. Yet the locations and structural consequences of linker histone binding are still enigmatic. Here, using cryo-atomic force microscopy, we show that the linker histone H5 in native chromatin and in chromatosomes reconstituted on the 5S rDNA template is located at the dyad of the nucleosome core particle, within the "stem" structure. Direct measurement also indicates that the length of free linker DNA between chromatosomes in native chromatin is approximately 30 bp, slightly shorter than that estimated from nuclease digestion assays.