Proteins in chromosome banding. I. Effect of G-banding treatments on the proteins of isolated nuclei.

Nuclei were isolated from Chinese hamster cells, treated with hypotonic KCl, fixed in acetic methanol, and either air-dried in glass tubes (in situ) or left in suspension (in vitro). These preparations were then exposed to a variety of G-banding treatments, including the 2 xSSC, urea, NaCl-urea, and trypsin methods. The proteins extracted into the treatment solution and those remaining in the nuclei were analyzed by SDS polyacrylamide gel electrophoresis. The three former treatments extracted specific subsets of the total nuclear nonhistone proteins into the treatment solution. Some of the extracted nonhistones were common to all treatments while others were unique to a particular treatment. Variable amounts and types of the histones were also extracted by these treatments, but significant quantities of all of these proteins still remained in the nuclei afterwards. The trypsin treatment appeared to degrade some of the nonhistones, while other nonhistones, as well as the histones, were relatively resistant to trypsin digestion. Although there were a few differences in the residual proteins found in the nuclei after the various G-band treatments, the overall electrophoretic patterns of these proteins were generally similar. The results indicate that the G-banding techniques induce specific and reproducible changes in the proteins of isolated nuclei. If these banding treatments induce similar changes in the proteins of mitotic chromosomes, such alterations might be involved in mechanisms of chromosome banding.