Proteins in chromosome banding

Abstract

SDS polyacrylamide gel electrophoresis was used to study the proteins extracted from, and those remaining in isolated, fixed, air-dried nuclei subjected to a variety of R- and C-banding techniques. The R-banding procedures, involving exposure to hot Earle's BSS or NaH₂PO₄, had the least effect of any of the banding techniques on the extraction of proteins from isolated nuclei. Only small amounts of 5 nonhistone proteins were detected in the Earle's BSS extract, and no proteins were found in the NaH₂PO₄ solution after treatment. The residual proteins remaining in the nuclei after either treatment were virtually identical to those in control nuclei. The C-banding techniques, on the other hand, produced substantial changes in the nuclear proteins. These techniques involve several sequential steps, including HCl treatment, exposure to NaOH or Ba(OH)₂, and an incubation in hot SSC. The HCl treatment extracted some of each of the histones and a few nonhistones; the NaOH extracted a large variety of nonhistones and some of each of the remaining histones. No proteins were detected in the SSC solution. Some of the proteins extracted by Ba(OH)₂ appeared to be degraded. A comparison of the residual proteins left in the nuclei after the two complete C-banding treatments revealed both similarities and differences. The Ba(OH)₂ technique appeared to have a more severe effect on the nuclear proteins than the NaOH technique. Fewer residual nuclear proteins were observed after the former technique, but all of these were also represented in nuclei after the NaOH technique. The results indicate that the different treatments producing a common type of banding generally have similar effects on the nuclear proteins, while the treatments producing different types of banding (G-, R-, C-banding) have substantially different effects on these proteins. Such alterations may have implications for chromosome banding.