We have studied the effect of sodium-n-butyrate on endogenous RNA polymerase in Physarum polycephalum. 1 mM butyrate strongly reduces RNA polymerase activity measured in isolated nuclei or chromatin; both RNA polymerase A as well as the alpha-amanitin sensitive RNA polymerase B are equally affected. Despite a concomitant hyperacetylation of histone H4 the template activity of chromatin, as analyzed by in vitro transcription of the chromatin with exogenous RNA polymerase from E. coli or RNA polymerase II from wheat germ, remains unaltered as compared to untreated control chromatin, indicating that there is no positive correlation between histone acetylation and template activity of chromatin for transcription in this organism. The results further indicate, that butyrate acts primarily as a quick but reversible inhibitor of protein synthesis in Physarum; the fast decrease of endogenous RNA polymerase activity after butyrate treatment is due to inhibition of enzyme synthesis rather than inactivation of other factors necessary for transcription.

Acetylation↗

PubMed1984

Depression of histone acetylation by alkylating antitumor agents: significance for antitumor activity and possible biological consequences.

Treatment of Ehrlich ascites tumor cells with the alkylating antitumor agents triaziquonum, N-mustard and cyclophosphamide leads to a reduction in the posttranslational incorporation of 3H-acetate into histones and the extent of histone acetylation in Ehrlich ascites tumor cells. All core histones are affected. The depression of histone acetylation is not the result of a decrease in acetyl-CoA. Evidence is presented for an activation of histone deacetylase by alkylating agents. A reduction of histone deacetylation is observed after exposure to all concentrations of alkylating agents which inhibit cell proliferation. In order to evaluate the biological consequences of a reduction of histone acetylation, the extent of acetylation was modulated by either chemical acetylation or treatment with butyrate. In all cases an increase in histone acetylation leads to an enhancement of the rate of transcription. In accord with previous reports from our laboratory (1), it is concluded that the reduction of histone acetylation affects RNA synthesis. It is emphasized, however, that besides a regulation of transcription, histone acetylation may be involved in other cell functions. Thus, the complete biological consequences of the reduction of histone acetylation remain to be elucidated. In view of the antitumor activity of the alkylating agents it seems noteworthy that hepatoma AS30D cells are characterized by a remarkably higher extent of histone H4-acetylation compared to normal, adult, fetal, or regenerating liver.

Alkylation↗

PubMed1984

Depression of histone acetylation by alkylating antitumor agents in murine cells.

Treatment of Ehrlich ascites tumor cells with the alkylating agent triaziquone [2,3,5-tris(ethyleneimino)benzoquinone-1,4] and nitrogen mustard leads to a reduction of the posttranslational acetylation of histones. Acetylation of all core histones is affected. The reduction of labeling of acetylated sites is accompanied by a dose-dependent decrease in the extent of acetylation as indicated by the level of acetylation of H4. The depression of histone acetylation is expressed at all concentrations of the alkylating agents which cause significant inhibition of tumor cell proliferation. It could be excluded that the observed effects are caused by an impairment of acetyl coenzyme A synthesis.

Acetates↗

PubMed1976

[Formation of pyridone derivates from maltose and lactose. XII. Investigations on the Maillard-reaction (authors transl)].

Maltose and lactose react with methylammoniumacetate in a hot aqueous solution giving a dark brown mixture of products. 1,2-dimethyl-3-hydroxy-4-pyridone (5) can be isolated from the volatile compounds. Maltol and Isomaltol can be converted into the pyridone 5 with methylammoniumacetate. 1-Carboxymethyl-3-hydroxy-2-methyl-4-pyridone is obtained from isomaltol and glycine.

Chemical Phenomena↗

PubMedDate not supplied

Lack of correlation between histone H4 acetylation and transcription during the Physarum cell cycle.

The interaction between nucleosomal proteins and DNA is expected to change during DNA replication as well as during transcription. A possible way of achieving the necessary structural changes is the modification of histones and high mobility group (HMG) proteins. The acetylation of core histones has been studied in various systems (for a review see ref. 1) and a correlation between histone acetylation and transcriptional activity of chromatin has frequently been proposed. In particular, Bradbury and co-workers have reported a cell cycle dependence of histone H4 acetylation in Physarum polycephalum which revealed two correlations: (1) tetraacetylated H4 (H4Ac4) correlated with the rate of transcription and (2) H4 acetylation was inversely correlated with H1 phosphorylation in mitosis. We present evidence here that H4 acetylation does not fit these correlations. Our data clearly show that the acetate content of H4 is high during the S phase, but low during later stages of the cell cycle. H4Ac4 remains at a nearly constant level during the whole cycle, with an elevation during the S phase. Furthermore, experiments with the deacetylase inhibitor sodium-n-butyrate do not support the proposed connection between diacetylated H4 (H4Ac2) and DNA replication. Our data imply that a correlation of H4 acetylation and transcription is unlikely during the cell cycle of Physarum. The conclusions of Bradbury and co-workers are therefore invalid.

Acetylation↗