Nonhistone chromosomal proteins in control of cell division

Nonhistone chromosomal (NHC) proteins have been shown to play a major role in the control of cell proliferation. An early increase in the synthesis of NHC proteins has been demonstrated in confluent WI-38 fibroblasts stimulated to divide by a change of medium containing 10% serum. This increase precedes by 30 min an increase in the template activity of chromatin from stimulated cells, whether assayed with E. coli or homologous RNA polymerase. Inhibition of NHC protein synthesis by cycloheximide inhibits the increase in chromatin template activity. Further, chromatin reconstituted with NHC proteins from stimulated cells has a higher template activity than chromatin reconstituted with NHC proteins from unstimulated cells. These findings have led to the conclusion that the NHC proteins synthesized in response to stimulation in WI-38 cells are responsible for the increase in chromatin template activity and for the stimulation of cell division. If true, the removal from chromatin of NHC proteins synthesized in response to stimulation should also cause the disappearance of the increase in chromatin template activity. The authors report that both the NHC proteins synthesized in response to stimulation as well as the increase in chromatin template activity can be easily removed by washing the chromatin with low concentrations of NaCl.