Rapid transfer of non-histone chromosomal proteins to the nucleus of living cells.

Abstract

CHROMATIN of eukaryotic cells is composed of DNA, histones and non-histone chromosomal proteins. Histones are generally thought to be nonspecific gene repressers and components maintaining the structure of chromatin. On the other hand, recent reports suggest that non-histone chromosomal proteins activate regions of repressed DNA by their association with histones1. This idea was mainly derived from studies at the transciptional level with reconstituted chromatin in vitro2. The ultimate function of biological substances in cells might be determined by injecting these substances directly into living cells. Accordingly, we recently developed a method for introducing macromolecules into culture cells using erythrocyte ghosts (ghost fusion method)3; the method is based on virus-induced cell fusion of resealed erythrocyte ghosts containing the substance with recipient cells. To obtain clues to the function of non-histone chromosomal proteins inside cells, we have now used this method to introduce iodine-labelled non-histone chromosomal proteins from rat liver into mouse cells and then studied distribution of these proteins in the recipient cells. We found that they were rapidly transferred to the cell nuclei.