Isolated metaphase chromosomes: scanning electron microscopic appearance of salt-extracted chromosomes.

Scanning electron microscopy of salt extracted, isolated metaphase chromosomes has been used to further the understanding of the role of proteins and DNA in chromosome architecture. Metaphase chromosome surfaces consist of numerous compact microconvules with an average diameter of 520 +/- 78 A which result from several orders of supercoiling. Treatment of isolated chromosomes with various salt concentrations ranging from 0.4 to 2.0 M NaCl revealed a longitudinal array of fibres within the chromatids as well as regions of coalesced nucleoprotein. The results demonstrate sensitivity of chromosome structure based on chromatin supercoiling, to progressive extraction of chromosomal proteins and DNA over the range of salt concentrations examined.