Atomic force microscopy study of chromosome surface structure changed by protein extraction.

We applied atomic force microscopy (AFM) to investigate the surface structure of barley chromosome in combination with a chemical treatment method. As a result, we have obtained high-resolution topographic images of granular structures with a diameter of ca. 50 nm on the surface of critical-point dried metaphase chromosomes. Treatment with 2M NaCl significantly modified the chromosome surface structure: surface roughness was increased and chromosome thickness was decreased. The NaCl treatment extracted two major proteins with molecular weights of 4000 and 20,000 Da. These proteins might be belonging to non-histone protein families that do not contain any aromatic amino acid. The results demonstrate the advantage of the combined method of high-resolution AFM imaging and chemical treatments for understanding nano-scale surface structures of the chromosome.