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P Loidl

Publications and source records attributed to P Loidl.

65 records · Page 4Linked to original sources
PubMed1985

An immunological approach to enrich a mitotic stimulator and to reveal G2-phase-specific proteins in Physarum polycephalum.

Purified antibodies from an antiserum against S-phase proteins of the myxomycete Physarum polycephalum were attached to protein-A-Sepharose CL-4B. A late G2-phase extract that contained a mitosis-stimulating protein was applied to this immunoadsorbent, and the mitosis-stimulating protein was enriched by a factor of ten. This protein, which is present in the cell in low amounts, is synthesized in late G2 phase and obviously degraded in a later stage of the cycle. Immunoadsorption of a G2-phase extract with anti-S-antibodies decreased the 700 main proteins to 20 as demonstrated by two-dimensional gel electrophoresis. No difference in protein pattern could be observed on two-dimensional gels between S-phase and G2-phase extracts before and after immunoadsorption with anti-S-antibodies. This indicates that there are no G2-phase-specific proteins among the 700 most abundant proteins of Physarum polycephalum.

Electrophoresis, Polyacrylamide Gel↗
PubMed1984

RNA polymerase activity and template activity of chromatin after butyrate induced hyperacetylation of histones in Physarum.

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

Thymidine kinase. A novel affinity chromatography of the enzyme and its regulation by phosphorylation in Physarum polycephalum.

dThd bound to epoxy-activated Sepharose results in a high specific affinity adsorbent, which was used to purify Physarum dThd kinase 8000-fold. With this purified enzyme, it was proved that dThd kinase exists in five enzyme variants in Physarum polycephalum, the acidic forms being phosphorylated. This protein modification is discussed under the aspect of the regulation of this enzyme.

Chromatography, Affinity↗
PubMed1983

Response of the dTMP-synthesizing enzymes to differentiation processes in Physarum polycephalum.

Synthesis of deoxythymidylate (dTMP) is a rate-limiting step in DNA synthesis; there are two main enzymes which are responsible for dTMP production, thymidylate synthetase (ts) and thymidine kinase (tk). Both enzymes were studied during several differentiation processes of the myxomycete Physarum polycephalum. In all stages of proliferation (microplasmodia, macroplasmodia, germinating microsclerotia and germinating spores) tk is the dominant enzyme in terms of activity, whereas ts is the predominant enzyme in quiescent stages (microsclerotia, sporangia, respectively spores); this is expressed by calculating the tk/ts ratio. This ratio is greater than 1 during proliferation and much less than 1 during quiescence. Our results clearly show that ts is the basic enzyme for dTMP production during all differentiation stages, whereas tk, if required, is shut on and represents an additional potential for dTMP synthesis during rapid proliferation.

Butyrates↗
PubMed1982

Thymidylate synthetase during synchronous nuclear division cycle and differentiation of Physarum polycephalum.

Thymidylate synthetase and thymidine kinase activities in wild type strain M3b and in thymidine kinase-deficient mutant TU63 of Physarum polycephalum are studied. Whenever nuclear division occurs in macroplasmodia of wild type, thymidine kinase and thymidylate synthetase activities sharply increase, although the increase of thymidylate synthetase activity is less pronounced than thymidine kinase activity. This is also true for other investigated nuclear divisions during the life cycle of P. polycephalum. It is shown for the first time that thymidylate synthetase is a periodically fluctuating enzyme during the naturally synchronous nuclear division cycle of P. polycephalum with a peak of specific activity in the S phase. In macroplasmodia, as well as after germination of microsclerotia of M3b, thymidine kinase is the dominant enzyme, whereas at the time of the precleavage mitosis in sporulating macroplasmodia thymidylate synthetase is the predominant enzyme. This study describes and compares both dTMP-synthesizing enzymes during proliferation and differentiation of the same organism.

Cell Cycle↗
PubMed1982

Cell-cycle-dependent effects of sodium-n-butyrate in Physarum polycephalum.

Sodium-n-butyrate affects the length of the mitotic cycle of Physarum polycephalum. Application during S- or early G2-period results in a delay of the subsequent mitosis, whereas application later in the cycle has no delaying effect. Interestingly, the second mitotic cycle after application is considerably shortened when butyrate has been administered during S- or early G2-period of the preceding cycle. In comparison, other homologous short-chain fatty acids were tested; the retarding effect on mitosis increases with the number of carbon atoms, although only butyrate can shorten the second mitotic cycle. It is shown that butyrate causes an immediate depression of synthesis of DNA, RNA and protein. After a certain time-interval the plasmodium overcomes the butyrate block. DNA synthesis is fully recovered and the inhibition of RNA and protein synthesis is even overcompensated until the next mitosis, as reflected by elevated levels of RNA and protein.

Butyrates↗
PubMed1982

Control of mitotic synchrony in Physarum polycephalum. Phase shifting by fusion of heterophasic plasmodia contradicts a limit cycle oscillator model.

Fusion of two multinuclear plasmodia of Physarum polycephalum representing different stages of the mitotic cycle causes a rapid mitotic synchronization of "young" (A) and "old" (B) nuclei [2, 14, 19]. This communication reveals that even at large phase differences synchronization always occurs by advancing "young" and retarding "old" nuclei. This strongly contradicts a limit cycle oscillator model [8] which would permit synchronization on the shorter arc of the phase circle (advancing B and retarding A) at phase differences larger than 1/2 of the cycle. Density labelling of newly synthesized DNA in mixed plasmodia with BdUrd indicates that G2-nuclei become irreversibly committed for mitosis and DNA synthesis at a transition point located within only a few minutes of the visible onset of chromosome condensation.

DNA, Fungal↗
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↗