Visualization of chromatin folding patterns in chicken erythrocytes by atomic force microscopy (AFM)

Abstract

The organization of the higher order structure of chromatin in chicken erythrocytes has been examined with tapping-mode scanning force microscopy under conditions close to their native environment. Reproducible high-resolution AFM images of chromatin compaction at several levels can be demonstrated. An extended beads-on-a-string (width of ∼ 15-20nm, height of ∼ 2-3nm for each individual nucleosome) can be consistently observed. Furthermore, superbeads (width of ∼ 40nm, height of ∼ 7nm) are demonstrated. Visualization of the solenoid conformation at the level of 30nm chromatin fiber is attained either by using AFM or by using electron microscopy. In addition, tightly coiled chromatin fibers (∼ 50-60nm and ∼ 90-110nm) can be revealed. Our data suggest that the chromatin in the interphase nucleus of chicken erythrocyte represents a high-order conformation and AFM provides useful high-resolution structural information concerning the folding pattern of interphase chromatin fibers.