Abstract
Histone fractions prepared from various sources stimulated DNA synthesis in quiescent BALB/ 3T3 cells in sparse culture. Of the various sources investigated, the stimulatory activity was highest in the histone fraction prepared from rat Rhodamine fibrosarcoma. The maximal activity at optimal concentration of the histones from the tumor was about half that in the presence of an excess concentration of calf serum. The histone fraction was fractionated by column chromatography on Bio-Gel P-60. All histone species thus obtained had stimulatory activity for DNA synthesis.Although protamine, poly-L-lysine and poly-L-arginine also stimulated DNA synthesis in BALB/ 3T3 cells, the former two polypeptides were less effective than any of the histones.In addition, we found that the nonhistone protein fraction from tumor chromatin stimulated DNA synthesis in BALB/ 3T3 cells. The maximal activity at optimal concentration of nonhistone protein corresponded to that achieved by excess calf serum. From these findings, we postulate the role of a growth factor located in cell nuclei in controlling cell proliferation.
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