Nuclear nonhistone proteins in murine melanoma cells. I. Quantitative isolation and fractionation.

Nuclear nonhistone proteins (NHP's) have been implicated as regulatory agents involved in controlling genetic expression. Utilizing murine melanoma cells, we describe a method for isolating and fractionating NHP's which greatly increases the yield of these proteins as well as the level of resolution required for detecting small differences in particular NHP's. Mouse melanoma cells were grown in medium labeled with [(3)H]leucine. Following 48 hr of incubation, the cells were harvested and nuclei isolated. The NHP's were extracted from the nuclei in a series of steps which yielded four major fractions: NHP(1), NHP(2), NHP(3), NHP(4). This method solubilized 80-90% of the protein from the nuclear homogenate. The NHP fractions were then separated on DEAE-cellulose columns in a series of salt steps increasing in concentration from 0.05 to 0.50 M NaCl, followed by steps of 2 M NaCl and 4 and 7 M guanidine-hydrochloride. The 40 NHP fractions eluted from these columns were further separated on polyacrylamide-SDS gels and ranged in molecular weight from 9000 to 110,000 daltons. Differences were observed in the electrophoretic pattern of each of these 40 fractions. The high resolution of these fractionation procedures greatly enhances the possibility of observing small changes in proteins which may play a role in gene regulation.