[The presence of glycosyltransferases on chromatin acceptors in monkey liver nuclear membranes (author's transl)]

Evidence for incorporation of N-acetylglucosamine in endogenous nuclear acceptors during the nuclear matrix preparation

1. The presence of glycoproteins within the nucleus of cell is now well established and the question arises on the nature of the nuclear glycosylation and the site of their glycosylation. 2. In order to study endogenous nuclear proteins acceptors, we have isolated a subnuclear fraction: nuclear matrix characterized by DNA, RNA, phospholipids and proteins content. Nuclear matrix acceptors were obtained from nuclei incubated with UDP-N-acetyl [14C]glucosamine. 3. In this report we describe the presence of three major glycoproteins labeled with N-acetyl [14C]glucosamine in the nuclear matrix fraction. We obtained gP32, gP67 and gP70 with pI values around 6.2, 6.5 and 8.2.

Transfer of N-acetylglucosamine to nuclear endogenous acceptors of rat hepatocytes

1. Nuclei were prepared from rat hepatocytes. A biochemical analysis of marker enzymes showed that the nuclei are not contaminated by other subcellular fractions, especially endoplasmic reticulum. 2. The transfer of [14C]N-acetylglucosamine to endogenous acceptors were studied comparatively in the nuclei and in the other subcellular fractions of rat hepatocytes. 3. In this report we describe the presence of the transfer of N-acetylglucosamine within the nucleus of rat hepatocytes. We found 21% of this transfer in the nucleus fraction with an enrichment of 26 in comparison to homogenate.

Rat testes interstitial cell nuclei exhibit three distinct receptors for retinoic acid

Purified nuclei from rat testes interstitial cells were incubated with an equimolar complex of [3H]retinoic acid and purified cellular retinoic acid-binding protein (cRABP) and with ATP. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and radiofluorographic analysis of the nuclear fractions indicated the presence of 3 highly labeled receptors for retinoic acid which were distinct from cRABP. These data demonstrate that retinoic acid binds to 3 novel nuclear acceptors of which cRABP does not appear to be a part.

Kinetics of subcellular distribution in rat intestine of 1,25-dihydroxycholecalciferol administered in vivo. Evidence for concentration within 5 min into purified nuclei

To better understand the initial steps in the induction of intestinal Ca2+ transport by 1,25-dihydroxycholecalciferol [1,25(OH)2D3], we studied the early subcellular localization of 1,25(OH)2D3 in rat intestine. Vitamin D-deficient rats received 300 pmol of 1,25(OH)2[3H]D3 intravenously at 5 min to 4h before being killed. Cells homogenized in buffer of I = 90 mmol/litre were fractionated by centrifugation into a crude nuclear pellet, purified nuclei, Golgi and basal-lateral membranes, cytosol and a post-nuclear pellet. Nuclear purification was established by biochemical and morphological criteria and gave a yield of 32 +/- 2% (mean +/- S.E.M.; n = 21). Although re-establishment of Ca2+ uptake by Golgi is one of the earliest reported intestinal responses to 1,25(OH)2D3, no direct localization of 1,25(OH)2D3 to Golgi was detected. Purified nuclei had the highest specific radioactivity at all times studied, with nuclear localization detectable at 5 min and peak nuclear uptake at 1 h. Relative specific radioactivity of nuclei to cytosol increased from 5 min to 30 min, at which time equilibrium between cytosol and nucleus appeared to be attained. Nuclear uptake occurred in all cells from villus to crypt. Of total nuclear binding 10% was resistant to high ionic strength buffer (I = 365 mmol/litre); peak nuclear uptake was observed at 30 min in this buffer. This tight binding may represent the active fraction of 1,25(OH)2D3. These results indicate that localization of 1,25(OH)2D3 to rat intestinal nuclei precedes the observed Golgi-membrane effects and suggest the existence of high-affinity nuclear 1,25(OH)2D3-binding sites.

Evidence of the mannosylation of a non-histone protein in monkey liver chromatin

Mannose is incorporated in monkey liver chromatin by the means of a nuclear membrane mannosyltransferase. 14C-labelled chromatin is dissociated either by sulfuric acid or 6 M urea and 0.4 M GuCl. The fractions then enriched in non-histone 14C-labelled proteins are excluded from Ultro-gel AcA 202, their analysis in SDS-polyacrylamide gel electrophoresis shows that radioactivity fits with one major protein band, confirming the presence of at least a non-histone protein labelled with mannose in monkey liver chromatin, with an apparent molecular weight of 13,000.