The electron-microscopic structure of nucleoprotein fibrils from metaphase chromosomes treated with salt

The diameter of nucleoprotein fibres of metaphase chromosomes is sensitive to salt concentrations. Treatment of human lymphocyte cells in metaphase with a hypotonic medium and spreading them on a water surface causes swelling of the chromosome fibres from 150–180 Å to 230–250 Å. Treatment of the chromosomes with 0.15–0.45 M NaCl, a concentration at which histones are not yet removed from the nucleoprotein complexes, apparently does not affect the chromosome structure. Treatment with NaCl solutions between 0.6 M and 2.0 M NaCl leads to a progressive extraction of the chromosomal proteins and decreases the diameter of the chromosome fibres to 80–100 Å and less.Dedicated to Prof. Dr. A. Butenandt on the occasion of his 70th birthday.