Regulation of transcription by DNA-bound non-histone nuclear proteins

ADP-ribosylation of proteins in brain regions of rats during postnatal development

Post-translational modifications of chromatin-bound proteins play an important role in the regulation of eukaryotic gene expression. Processes such as acetylation, methylation, phosphorylation and ADP-ribosylation may alter the interaction of these proteins with DNA and consequently affect chromatin conformation and the binding of enzymes and other molecules involved in the regulation of gene expression. In the present study the process of ADP-ribosylation of chromosomal proteins (histone and non-histone proteins) in some rat brain regions during postnatal development was investigated; also the effect of epidermal growth factor (EGF) on this process in fetal brain slices was studied. It has been found that the process of ADP-ribosylation of total histones extracted from rat cerebral cortex and cerebellum at 1, 10 and 30 days of age, increases from 1 to 10 days of age (i.e. the period of maximal cell proliferation) and decreases thereafter, while the process of ADP-ribosylation of non-histone proteins (NHPs) sharply decreases during the same developmental period. The addition of EGF to fetal brain slices causes a significant increase of ADP-ribosylation of total histones (particularly of the histone H1 fraction) and also of NHPs and microsomal proteins. This result is in agreement with the effect of EGF as a mitogen factor, previously shown in astroglial cell cultures.

Chromatin proteins associated with micrococcal nuclease-sensitive and nuclease-resistant chromatin fractions of Kirkman-Robbins hepatoma and hamster liver

Micrococcal nuclease-sensitive (SP) and nuclease-resistant (PP) chromatin fractions from Kirkman-Robbins hepatoma and hamster liver were obtained. The molecular distribution of three non-histone proteins (NHCP1, NHCP2 and NHCP3), histones, and chromatin-bound protease activity between SP and PP fractions of both tissues was compared. Differences, mainly of quantitative nature, among non-histone proteins of neoplastic and normal tissue were observed. Moreover, it was found that polypeptides with mol. wt 81 000 (NHCP1), 39 000 (NHCP2) and 21 000, 35 000, 37 000 (NHCP1), 70 000, 112 000, 141 000, 157 000 (NHCP2), 30 000-33 000 (NHCP3) were associated only with the nuclease-sensitive part of chromatin of hepatoma and normal tissue, respectively. A major difference in histone composition of hamster hepatoma and liver concerns histones H2A and H1. Furthermore, an enrichment of high mobility group proteins as well as other soluble non-histone proteins in an acid extract of the SP fraction was observed. Apparently chromatin-bound protease activity can be found in both fractions of chromatin.

Chicken liver non-histone protein fraction repressing DNA transcription in vitro

A chicken liver non-histone protein fraction repressing DNA transcription in vitro was isolated using ultrasound shearing followed by precipitation with divalent cations. It was characterized by SDS-polyacrylamide electrophoresis and isoelectric focusing. This inhibitory protein fraction showed strong affinity to DNA and represented non-histone proteins with main bands of mol. wt about 35000 and 56000 and isoelectric points about 5.7 and 6.2. The inhibitory non-histone protein fraction seems to repress DNA transcription by interacting with DNA template rather than with RNA polymerase.

Distribution of non-histone proteins between micrococcal nuclease sensitive and nuclease resistant chromatin from chicken cells with active and inactive genomes

Chicken liver and erythrocyte nuclei were separated by mild treatment with micrococcal nuclease into nuclease sensitive (NS) and nuclease resistant (NR) fractions, differing in chemical composition and transcriptional activity in vitro. Nuclei, NS and NR fractions of both tissues were fractionated by hydroxyapatite chromatography into three groups of non-histone chromatin proteins (NHCP) and characterized by SDS-polyacrylamide gel electrophoresis. Some differences in the molecular distribution of non-histone proteins of chicken liver and erythrocytes between nuclease sensitive and resistant parts of chromatin have been described.

Post-translational changes of chromosomal proteins in rat cerebellum during postnatal development

Acetylation, phosphorylation and methylation of nuclear proteins in rat cerebellum at 10 and 30 days of age were investigated in vitro. Isolated nuclei were incubated in the presence of [1-14C]acetyl CoA, S-adenosyl [methyl-3H]methionine and [gamma-32P]ATP and then separated into histones and non histone proteins (NHP), which were further fractionated by polyacrylamide gel electrophoresis. The results obtained indicate that acetylation, phosphorylation and methylation of both basic and acidic proteins decrease from 10 to 30 days of age. Electrophoretic analysis of histones shows that the decrease mainly concerns H1, H3, and H2b fractions. The H3 fraction is always more labeled than the other fractions and shows the major changes during postnatal development. Phosphorylation of H2a and H4 fractions increases from 10 to 30 days of age, whereas acetylation and methylation of these fractions do not show significant changes from 10 to 30 days. The densitometric and radioactive patterns of NHP show considerable changes between 10 and 30 days, especially in the high molecular weight region. The incorporation of 14C-acetyl and 3H-methyl groups and of 32P phosphate appears to be generalized throughout the molecular weight range and decreases from 10 to 30 days of age. The methylation of an as yet unidentified protein with a molecular weight of approximately 110,000 daltons occurred at both ages.

Posttranslational modifications of nuclear proteins in rat cerebral hemispheres during postnatal development

The processes of acetylation, phosphorylation, and methylation of nuclear proteins in cerebral hemispheres of 10- and 30-day-old rats were investigated. The experiments were carried out in vitro by measuring the incorporation of labeled precursors into histones and nonhistone chromosomal proteins (NHP) extracted from nuclei and separated by polyacrylamide gel electrophoresis. The results obtained indicate that there are age-specific differences in the processes of phosphorylation and methylation of chromosomal proteins, whereas the acetylation process did not change significantly between 10 and 30 days of age. Electrophoretic analysis of histones indicated that the histone H3 was labeled to a greater degree than the other fractions and showed major changes in the processes of phosphorylation and methylation during postnatal development. The electrophoretic analysis of NHP showed considerable changes between 10 and 30 days of age. Certain components of NHP became increasingly evident as the brain developed. The methylation of an as yet unidentified protein with a molecular weight of approximately 118,000 daltons occurred at both ages.

Distribution of chromatin proteins between fractions of hamster liver chromatin differing in their susceptibility to micrococcal nuclease

Hamster liver nuclei were fractionated by digestion with micrococcal nuclease into nuclease released (SP) and nuclease resistant (PP) fractions varying in chemical composition and transcriptional activity. Electrophoretic analysis of histones from SP and PP showed no qualitative and quantitative differences. Apparently chromatin-bound protease activity can be found in both fractions. Nonhistone chromatin proteins isolated from SP and PP under mild conditions were fractionated by hydroxyapatite chromatography into NHCP1, NHCP2, NHCP3 and molecular heterogeneity and specificity were tested by SDS-polyacrylamide gel electrophoresis. The differences observed in nonhistone proteins are mainly of quantitative nature, however some specific polypeptides for SP and PP are observed.

Biochemical characterization of a specific phosphate acceptor of nuclear cyclic AMP-independent protein kinase

The regulatory mechanism of transcription involved in the phosphorylation of a 13 kDa non-histone chromatin protein from calf thymus, which is the most effective phosphate acceptor for cyclic AMP-independent protein kinase purified from the nuclei of mouse spleen cells, by the kinase has been studied in vitro. An analytical study of the circular dichroism (CD) spectra of the 13 kDa protein under different conditions showed that it underwent a major conformational change when incubated with DNA. The presented data suggest that the DNA-induced conformational change may result in a great increase of the 13 kDa protein phosphorylation by the kinase in vitro. Mg2+ (8-10 mM) enhanced the binding of the protein to DNA. Furthermore, the phosphorylated 13 kDa protein stimulated elongation of RNA synthesis by RNA polymerase II from calf thymus. However, neither the 13 kDa protein nor the phosphorylated 13 kDa protein had any affect on DNA synthesis. The available evidence suggests that the 13 kDa protein may play a role in the regulation of transcription through its phosphorylation by the kinase in vitro.

Phosphorylation of chromatin proteins in cerebral anoxia and ischemia

Phosphorylation of nuclear protein was investigated in cerebral anoxia up to 30 min with rabbit brain and in cerebral ischemia up to 6 h with gerbil brain in vitro. Isolated nuclei were incubated in the presence of [gamma-32P]ATP and were then fractionated into the NaCl-soluble, HCl-soluble, and phenol-soluble protein fraction. Each protein fraction was further separated by gel electrophoresis, and profiles of 32P incorporation were evaluated in these pathophysiological conditions. 32P incorporation of the acidic phenol-soluble nonhistone chromatin protein became significantly suppressed in cerebral anoxia after 15 min, and there were decreases of 32P incorporation in protein with high molecular weight and increase in protein with low molecular weight on gel electrophoresis. With gerbil brain nuclei, 32P incorporation into the NaCl-soluble and HCl-soluble fraction was increased without significant decrease in the phenol-soluble fraction after an ischemic period of 3 h. However, further separation of the phenol-soluble fraction demonstrated decrease of 32P incorporation in protein with high molecular weight and increase in protein with low molecular weight. At present, the significance of these findings, particularly in relation to chromatin template activity or irreversibility of these pathophysiological conditions, is not clear.

Comparative studies on chromatin proteins from chicken thrombocytes and erythrocytes

Comparative studies on chromatin composition, nature of non-histone chromatin proteins, histone fractions and the activity of chromatin-bound protease from chicken thrombocytes and erythrocytes were performed. Chemical analysis of chromatin preparations indicated the lack of an essential difference in the protein/DNA ratio. Analysis of non-histone chromatin proteins in SDS-polyacrylamide gel electrophoresis and isoelectric focusing showed a striking similarity of their electrophoretic patterns. Quantitative rather than qualitative differences predominated. During acidic urea-polyacrylamide gel electrophoresis, it was found that histones from thrombocytes contain a fraction migrating with the electrophoretic mobility of histone H5 from erythrocytes. This fraction constitutes 6.7% and 19% of total histone in thrombocytes and erythrocytes, respectively. The electrophoretic patterns of histones, as well as the amount of peptides soluble in 25% trichloroacetic acid released during incubation of chromatin and isolated histones at pH 8, indicated that the activity of chromatin-bound protease was significantly higher in thrombocytes than in erythrocytes.

Interaction of non-histone proteins with DNA and chromatin from Drosophila and mouse cells. Specificity, isolation and analysis of complexes

The specificity of the binding of purified non-histone proteins to DNA has been investigated through two types of experiments. Using a nitrocellulose filter assay at a low protein/DNA ratio, the binding of mouse non-histone proteins to mouse DNA was twice as great as the binding of mouse non histone protein to Drosophila DNA. The reverse experiment using Drosophila non-histone protein confirmed the interpretation that some protein . DNA complexes were specific. Protein . DNA complexes isolated by gel filtration chromatography indicated that 20% or 10% of the non-histone protein was bound to homologous or heterologous DNA respectively. Purified non-histone proteins bound with lower efficiency (15%) than unpurified but with higher specificity to soluble chromatin than to naked DNA. This binding did not result from an exchange between chromatin non-histone proteins and purified non-histone proteins added in excess. DNA-bound and chromatin-bound proteins were analysed on polyacrylamide gels. Whereas no major qualitative differences were observed with DNA-bound proteins, some proteins bound to homologous mouse chromatin were different from those bound to heterologous Drosophila chromatin. These results suggest a possible role of DNA-bound non-histone proteins in the regulation of gene expression.