SEM images of DNA double helix and nucleosomes observed by ultrahigh-resolution scanning electron microscopy.

We observed DNA double helix and nucleosomes in the chromatin of chicken erythrocytes by ultrahigh-resolution scanning electron microscopy. Specimens were prepared according to a modified microspreading technique in combination with the carbon plate method and observed without metal coating. A part of the DNA fibers without nucleosomes showed "left-handed" double-strands with twisting appearances and regular periodicities of the helix. Linker DNA between the nucleosomes showed "right-handed" appearances. Most of the nucleosome particles appeared as prolate ellipsoidal shapes of various sizes. DNA appeared to enter and exit the nucleosome particles on opposite sides winding around the histone core.