Synthesis Of Non-histone Chromosomal Proteins Research Articles

The effect of dimethylnitrosamine on the synthesis of high-mobility group non-histone proteins in regenerating rat liver.

A single injection of dimethylnitrosamine (DMN) given to adult rats induces hepatocellular carcinoma if given during the period of restorative hyperplasia following partial hepatectomy. The effect of DMN on the sequence of biochemical events in regenerating liver is therefore of interest. As carcinogenesis is likely to involve a change in control of gene expression, and as evidence suggests that non-histone chromosomal proteins (NHP) are involved in gene control, the effect of DMN on synthesis of NHP in regenerating liver was studied. A well-defined group of NHP, the high mobility group (HMG), known to be specifically associated with DNA active in transcription, were investigated. Partial hepatectomy was found to cause a large increase in incorporation of [3H]lysine into HMG proteins; this did not occur immediately, but was apparent at the time of DNA synthesis and of mitosis. DMN did not alter the relative amounts of different HMG proteins in relation to histone H1, but the carcinogen caused a considerable reduction in incorporation of [3H]lysine. This decreased synthesis of the proteins which may function as gene derepressors may well be relevant in carcinogenesis.

Effect of extradiol-17beta on the synthesis of specific uterine nonhistone chromosomal proteins.

The synthesis of specific nonhistone chromosomal proteins in the uterus of the ovariectomized rat was examined as a function of time after treatment with estradiol-17beta. Sequential stimulations in the rates of synthesis of at least five nonhistone chromosomal proteins having molecular weights of 96,000, 70,500, 29,400, 20,700, and 16,400, respectively, were observed. The rate of synthesis of the nonhistone chromosomal protein having a molecular weight of 70,500 was increased at 1 hr after hormone treatment. This was the first nonhistone chromosomal protein to be induced by estrogen, and its induction was blocked by pretreatment with actinomycin D. The data reported suggest but do not prove that this protein is the 4.5 S estrogen receptor, and that it is the induced nuclear acidic protein described earlier by Teng and Hamilton. The rates of synthesis of the nonhistone proteins with molecular weights of 96,000, 29,400, 20,700, and 16,400 were increased at 3,5,24, and 24 hr, respectively, after hormone treatment.

Gene activation in human diploid cells: Age-dependent modifications in the stability of messenger RNAs for nonhistone chromosomal proteins

Serum stimulation of early as well as late passages of nondividing WI-38 human diploid fibroblasts to proliferate, results in DNA synthesis beginning at 12 hours and mitosis at 20 hours. A 2-fold increase in the transcriptional activity of chromatin isolated from early and late passage WI-38 cells is evident one hour following serum stimulation. An increased synthesis and association with the genome of two defined molecular weight classes of nonhistone chromosomal proteins one hour following serum stimulation of early and late passage cells is also observed. The increased chromatin template activity and nonhistone chromosomal protein synthesis occur in early passage cells stimulated to proliferate in the presence of actinomycin D. However, when late passage WI-38 cells are stimulated in the presence of actinomycin D, increases in chromatin template activity and nonhistone chromosomal protein synthesis are not observed one hour following serum stimulation. The possibility that nonhistone chromosomal protein synthesis and activation of transcription early during the prereplicative phase of the cell cycle in early passage human diploid fibroblasts may be regulated at the translational level is discussed. Consideration is also given to the possibility that there may be an age-dependent modification in such a regulatory mechanism.

Stimulation of non-histone chromosomal protein synthesis in simian virus 40-infected simian cells

The pattern of synthesis of non-histone chromosomal proteins in simian virus (SV) 40-infected African green monkey kidney cells was analyzed by polyacryl-amide gel electrophoresis to see whether the changes in chromosomal protein metabolism are involved in the viral-induced synthesis of cellular DNA and mRNA. During the prereplicative phase of infection, the rate of histone synthesis was decreased until 15 h postinfection, whereas that of non-histone protein synthesis was increased after 5 h postinfection and reached a maximum at 10 to 15 h postinfection when viral-induced synthesis of cellular DNA and mRNA began to be observed. Stimulation of non-histone protein synthesis was also observed in the infected cells treated with cytosine arabinoside and was dependent on the multiplicity of infection. Stimulation occurred in almost all species of non-histone proteins. These results suggest that the stimulation of non-histone protein synthesis is caused by an early SV40 function and occurs prior to the viral-induced synthesis of cellular DNA and mRNA. During the replicative phase of infection, a marked increase in the rate of synthesis was observed in the non-histone proteins with molecular weights of about 48,000, 35,000, and 23,000, which were subsequently found to be SV40 capsid proteins.

Utilization of pre-existing messenger RNAs for nonhistone chromosomal protein synthesis in WI-38 human diploid fibroblasts

Contact-inhibited monolayers of WI-38 human diploid fibroblasts show an increase in chromatin template activity within 1 h following stimulation to proliferate. Direct evidence that nonhistone chromosomal proteins are responsible for this increased transcriptional activity of the genome comes from previous studies which demonstrate that the template activity of chromatin reconstituted with nonhistone chromosomal proteins from WI-38 cells 1 h following stimulation is higher than the template activity of chromatin reconstituted with nonhistone chromosomal proteins from contact-inhibited cells. The present studies indicate that there is an increase in the amount of two specific newly synthesized molecular weight classes of nonhistone chromosomal proteins in chromatin 1 h following the stimulation of contact-inhibited WI-38 cells to proliferate and that the synthesis of these nonhistone chromosomal proteins occurs in the absence of new RNA synthesis. The possibility that such nonhistone chromosomal protein synthesis early during the prereplicative phase of the cell cycle may be regulated at the translational level is discussed.

Effects of lysine deprivation and serum stimulation on the synthesis of non-histone chromosomal proteins by confluent chick fibroblasts

Chick embryo fibroblasts were cultured in vitro up to confluency, after which they were kept in the following different Minimum Essential Media containing a labelled amino acid: ( i) a medium containing 1% calf serum which prevented the cells from dividing; ( ii) a medium containing 30% calf serum which stimulated the cells to divide synchronously; ( iii) a medium without lysine but also containing 1% calf serum which prevented the cells to go beyond G 1. Chromosomal non-histone proteins (NHP) were extracted from cells cultured in these three different media and then were compared individually by gel electrophoresis. The gels were sectioned and the radioactivity measured in each slice. No significant variations were found in the level of radioactivity for individual resting cells ( i) if radioactive lysine (or leucine) was used as a precursor. A peak of radioactivity was observed before the onset of DNA synthesis for cells stimulated to divide ( ii). Whenever lysine was omitted for several hours ( iii) a peak of radioactivity was observed and was shown to be different from the peak found in stimulated cells. The rate of NHP synthesis under these various conditions was studied. Possible biological functions of the non-histone chromosomal protein were discussed.

The cell-cycle phase synthesis of non-histone proteins in mammalian cells

The synthesis of non-histone chromosomal proteins was studied as a function of cell-cycle position in synchronized Chinese hamster cells. Although non-histones were synthesized in all phases of the cell cycle studied, non-histone synthesis was 3–5 fold higher in late G 1 phase when compared to any other phase. Furthermore, separation of non-histones into molecular weight subgroups, using sodium dodecylsulfate-polyacrylamide gel electrophoresis, demonstrated that the high synthesis rates of late G 1 phase non-histones is principly characteristic of polypeptides larger than 45 000 daltons. Late G 1 cells inhibited from entering S phase for several hours by hydroxyurea, continued to synthesize non-histones at high rates. Upon removal of the hydroxyurea, non-histone synthesis rates decreased dramatically. This suggests that the synthesis of high molecular weight non-histone proteins is coupled to DNA synthesis.

Uncoupling of nonhistone chromosomal protein synthesis and DNA replication in human diploid WI-38 fibroblasts

Uncoupling of nonhistone chromosomal protein synthesis and DNA replication in human diploid WI-38 fibroblasts

Nonhistone chromosomal protein synthesis: utilization of preexisting and newly transcribed messenger RNA's.

Treatment of HeLa S(3) cells with actinomycin D during mitosis suppresses the synthesis of several major classes of nonhistone chromosomal proteins during the subsequent period before DNA replication, but allows the synthesis of other species of these proteins. Such results are consistent with the utilization of preexisting, as well as newly transcribed, messenger RNA's for nonhistone chromosomal protein synthesis during the prereplicative phase of the cell cycle.

Effect of nutritional changes on chromatin template activity and non-histone chromosomal protein synthesis in WI-38 and 3T6 cells

Quiescent confluent monolayers of WI-38 human diploid fibroblasts and of 3T6 mouse fibroblasts were stimulated to proliferate by nutritional changes. WI-38 cells had a stringent requirement for serum factor(s) but 3T6 did not require serum in order to proliferate again. In both cell lines there was an early increase in the synthesis of non-histone chromosomal proteins shortly after stimulation of cellular proliferation and this increase was linearly correlated to the number of cells entering the S phase several hours later. Only WI-38 diploid fibroblasts, however, showed an early increase in chromatin template activity 1 h after stimulation of cellular proliferation, while chromatin template activity in 3T6 cells remained unchanged. It is suggested that the activation of gene function represents a critical step for the passage of WI-38 cells in the G0 resting phase to the G1 phase of the cell cycle. It is also suggested that 3T6 cells are unable to enter or stay in a G0 phase but can be arrested predominantly in the G1 phase by nutritional deficit, probably amino acid starvation.

Continued synthesis of non-histone chromosomal proteins during mitosis

The synthesis of non-histone chromosomal proteins in synchronized HeLa S 3 cells was studied in 3 phases of the cell cycle: S, G 2 and mitosis. A 70–90% decrease in the rate of synthesis of total cellular protein and of chromatin-associated protein fractions extractable with low salt concentrations or with dilute acid was observed in cells in mitosis. On the contrary, the residual non-histone chromosomal proteins were synthesized during mitosis at a rate which did not differ significantly from that of S and G 2 phases. Thus, at variance with the other cellular proteins, acidic chromosomal proteins are synthesized at an undiminished rate even during mitosis, when there is complete cessation of RNA synthesis.