Differential phosphorylation of rat liver nuclear non-histone proteins in vitro

A pilot study on alterations of brain chromosomal protein phosphorylation by steroids during ageing

The modulatory effects of the steroid hormones estradiol-17 beta and hydrocortisone on phosphorylation of chromosomal proteins of the cerebral hemispheres (CH) of young and old rats was studied in vitro. The results indicate that the extent of phosphorylation decreases in both histone and non-histone-chromosomal (NHC) protein fractions as the age proceeds. Besides, both the hormones stimulate phosphorylation in young as well as old rats. However the pattern of stimulation shown by estradiol differs from that by hydrocortisone. In addition the extent of stimulation by these hormones is significantly reduced in old rats. Modulation of phosphorylation as provoked by these two hormones seems to play an important role in differential gene expression during ageing.

A chromosomal phosphoprotein is preferentially released by mild micrococcal-nuclease digestion

[32P]Pi was administered to rats (5mCi/rat) 2h before the isolation of liver nuclei. The isolated nuclei were subjected to mild micrococcal-nuclease digestion for 2.5, 5 and 10 min at 37 degrees C, and the mononucleosomal fraction was subsequently isolated by sucrose-density-gradient centrifugation. The specific radioactivity of 32P-labelled mononucleosomal fractions decreased with increased digestion times. A phosphorylated chromosomal protein, B2 (Mr 68000, pI6.5-8.2), was demonstrated immunologically in the mononucleosomal fraction by using an antibody specific to this electrophoretically purified phosphoprotein. The incorporation of 32P into this phosphoprotein, previously shown to be mainly through covalent linkage, was revealed by antibody precipitation followed by gel electrophoresis. The rate of release of acid-soluble nucleotides by micrococcal-nuclease digestion of liver nuclei from partially hepatectomized rats 16 h after operation was strikingly higher than that for sham-operated controls. After partial hepatectomy, an increase in 32P incorporation into phosphoprotein in the monomer fractions specifically precipitated by this antibody was also found. This suggests that the phosphorylated non-histone chromatin protein B2 is preferentially associated with the transcriptionally active chromatin.

Evidence for polyphosphate in phosphorylated nonhistone nuclear proteins

Structural studies of eucaryotic nuclear proteins have revealed the presence of bound polymeric phosphates. 32P-labeled and nonlabeled nonhistone nuclear proteins (NHPs) were isolated from rat liver nuclei and subjected to various controlled hydrolytic conditions. The analysis of protease-trypsin limit peptides revealed the presence of six phosphorylated, homogeneous fragments with phosphate/amino acid molar ratios greater than unity, ranging from 1.3 to 79. Alkaline beta elimination of phosphoester bonds released polymeric phosphates with chain lengths from 2 to over 200, as determined by using two-dimensional chromatographic analysis. The identity of these labeled polymeric phosphates was established to be polyphosphate by a number of criteria, including chromatographic mobility, gravimetric precipitation to constant specific activity, generation of orthophosphate on hydrolysis, and the determination of the delta H of hydrolysis of phosphoanhydride bonds. The evidence suggests that, in addition to the phosphomonoesters of serine and threonine, multiple phosphoanhydride linkages can result in the formation of polyphosphorylated NHPs. Previous investigators have demonstrated that exogenous, free polyphosphate causes destabilization of chromatin and enhancement of transcription in vitro. Although the function of the polyphosphorylated NHPs is currently unknown, such findings have possible functional implications with regard to the postulated role of NHPs as positive modifiers of gene expression.

Changes in the chromatin of the brain of developing rats: phosphorylation of chromosomal proteins and modulation of transcription

In vitro phosphorylation of chromosomal proteins and transcription of chromatin, and their modulation by spermine were studied by incubating slices of cerebral cortex of 3-30 day old developing rats with [32Pi] and [3H]-uridine, respectively. Phosphorylation of histones increases whereas that of nonhistone chromosomal (NHC) proteins decreases during development. Spermine stimulates phosphorylation of both histones and NHC proteins. Transcription of chromatin decreases as development progresses. Phosphorylation of chromosomal proteins stimulates transcription. This is further stimulated by spermine. However, these effects decrease as development proceeds. Such functional alterations in the chromatin may be responsible for the terminal differentiation of neurons, and may have a significant role in differential gene expression during cell differentiation and development.

Polyamines modulate phosphorylation and acetylation of non-histone chromosomal proteins of the cerebral cortex of rats of various ages

In vitro phosphorylation and acetylation of NHC (non-histone chromosomal) proteins and their modulation by spermine and spermidine were studied using slices of cerebral cortex of female albino rats of various ages. The total DNA, histone and NHC proteins do not change significantly with age. Phosphorylation and acetylation of total and individual NHC proteins decreases with increasing age of the rat. Spermine and spermidine stimulate phosphorylation and acetylation of specific NHC proteins in immature rats. This effect decreases with increasing age. It is suggested that such modulatory effects of polyamines may cause alterations in the expression of specific genes during aging.

Phosphodipeptide analysis of nonhistone nuclear proteins from Novikoff hepatoma ascites cells

To study the sites of phosphorylation in nuclear proteins a simple method was developed for the isolation and analysis of phosphodipeptides. Partial acid hydrolysates of unfractionated nonhistone nuclear proteins were subjected to Dowex-1 column chromatography followed by paper electrophoresis at pH 1.8. Phosphoserine- and phosphothreonine-containing dipeptides each had characteristic mobilities in the latter system. By subtractive Edman degradation these peptides were identified as having the general structure, X-PSer or X-PThr, where X is a nonphosphorylated amino acid. The two groups of phosphodipeptides were further purified into unique peptides by two-dimensional paper electrophoresis at pH 3.6 and 6.5. Amino acid analysis, and thus nearest neighbor analysis, of phosphodipeptides from nonhistone nuclear proteins revealed that a heterogeneous group of amino acids was on the amino terminal side of phosphoserine residues. In contrast, phosphothreonine residues were predominantly preceded by proline.