Changes in the phosphorylation of non-histone chromosomal proteins in relationship to DNA and RNA synthesis in BHK 21 C 13 cells

Abstract

We have compared the in vivo phosphorylation of the non-histone chromosomal (NHC) proteins in relation to nucleic acid synthesis, in cells stimulated to proliferate and in resting cells. When BHK 21C 13 cells in saturation density are stimulated to proliferate by a change of medium, a synchronized DNA synthesis occurs with a maximum at about 16 h. Early after stimulation the NHC protein phosphorylation increases and reaches a maximum in late G 1 before the onset of DNA synthesis. It remains high during early S and decreases in late S. The phosphorylation of total cellular proteins, on the contrary, is increased only at the time of maximum DNA synthesis and always remains lower than that of NHC proteins. Early after stimulation and through the G 1 phase an increase of total RNA synthesis is also observed, however the time of maximum RNA synthesis does not coincide with the maximum of NHC protein phosphorylation. The involvement of NHC protein phosphorylation in the regulation of some messenger RNA (mRNA) synthesis is discussed.