Biomedical subjects

R Jalouzot

Publications and source records attributed to R Jalouzot.

11 recordsLinked to original sources

PubMed1994

The NAD kinase: a phosphoryltransferase displaying an oxido-reductase activity--an electrophoretic study.

The search for a valuable technique for rapid detection, after electrophoresis, of the activity of various NAD kinase isoforms possibly present in different plant materials, has revealed interesting peculiarities of this enzyme (EC 2.7.1.23; also called ATP:NAD+ 2'-phosphotransferase). At first and in the unique but obligatory presence of NAD, the NAD kinase acts almost instantaneously as an oxido-reductase (probably coupled with the transformation of NAD to NADH). In the additional presence of ATP, the transformation of NAD+ to NADP+ reinforced such an oxido-reductase activity. Final assays testing for the specificity of the phosphoryl donor revealed that not only ATP but also GTP, G6P, and even NADP could be the substrate; the efficiencies of these phosphoryl donors varied with the different isoforms of NAD kinase, evidenced in the different seeds tested, and compared with NAD kinase from heterotropically grown Euglena cells, and NAD kinase purified from chicken liver (from Sigma Chemical Co.).

Adenosine Triphosphate↗

PubMed1985

Replication timing of the H4 histone genes in Physarum polycephalum.

The time of replication of the two H4 histone genes (H41 and H42) was determined during the naturally synchronous mitotic cycle of Physarum polycephalum. 5-Bromo-2'-deoxyuridine labeling and density gradient centrifugation was used to isolate newly synthesized DNA from defined periods of S phase. The DNA was analyzed by Southern hybridization with a cloned probe containing one of the H4 histone genes of Physarum. The results indicate that the two H4 histone genes are replicated in the first 30 min of S phase but not exactly at the same time. H41 is replicated during the first 10 min of S phase, when only 15% of the genome is duplicated, whereas H42 replicates between 20 and 30 min after the onset of S phase. The possible relationship between the periodic expression of the genes and the timing of their replication is discussed.

DNA Replication↗

PubMed1984

Histone H4 gene is transcribed in S phase but also late in G(2) phase in Physarum polycephalum.

The myxomycete Physarum polycephalum contains two types of H4 histone genes. Southern blotting of restriction endonuclease fragments of P. polycephalum DNA and hybridization to a cloned probe labelled by nick-translation indicate that there are only one or two copies of each H4 gene per haploid genome. A cloned homologous genomic probe was used to study the cellular abundance of H4 mRNA during the cell cycle. We report that the H4 mRNA is not only transcribed in S phase as previously described for other organisms but that transcription of the H4 gene also occurs at the end of G(2) phase. Since no translation of the histone messenger was observed in G(2) phase this suggests that the histone mRNA synthesized in G(2) constitutes a pool of molecules in anticipation of the next S phase.

Journal Article↗

PubMed1982

Physical relationship between replicons and transcription units in Physarum polycephalum.

Electron microscope spread preparations of nuclear chromatin derived from early S-phase of Physarum reveal 'beads on a string' for nonreplicated and a portion of newly replicated chromatin. Many of the early replicons contain transcription units as visualized by nascent transcripts. They are, in most cases, arranged in continuous length gradients on both newly replicated strands of chromatin, the putative origin of replication being within the transcription unit. Preferential release of DNA as acid precipitable material by DNAse I and of RNA polymerase B (estimated as release of labeled alpha-amanitin bound to isolated nuclei) is observed in early S-phase, but only if DNA synthesis is not inhibited. Also, generation of a small particle (peak A) by staphylococcal nuclease, characteristic of transcriptionally active chromatin, depends on concomitant replication of early replicons. It is concluded that DNA replication is a prerequisite for its transcription by RNA polymerase B. Thus, the sequential replication of the genome of Physarum dictates the order of transcription during S-phase which may in part control the proliferative mitotic cycle of Physarum.

Chromatin↗

PubMed1981

Multiple effects of 5 mM sodium butyrate on Physarum polycephalum macroplasmodia.

In a Physarum polycephalum macroplasmodium, nuclei naturally divide synchronously. Thus, it offers an opportunity to study growth and mitosis within a true organism. The effects of 5 mM sodium-butyrate on these processes have been examined. When this material is added to the culture medium during mitosis, the butyrate acts like a fixative on condensed chromosomes. During interphase, this short fatty acid stops growth and immediately inhibits DNA synthesis. Furthermore, it prevents differentiation in macroplasmodia induced to spherulate. All these modifications are readily reversible after transfer to a medium lacking butyrate.

Butyrates↗

PubMed1980

Kinetics of nuclease digestion of Physarum polycephalum nuclei at different stages of the cell cycle.

The kinetics of nuclease digestion of Physarum polycephalum nuclei by staphylococcal nuclease and DNase I has been studied at different stages of the cell cycle. Significant differences in the digestion behaviour of nuclei from metaphase and interphase have been detected with DNase I but not with staphylococcal nuclease. Furthermore the structure of newly replicated DNA in S phase differs from the bulk in that it is more easily degraded to acid-soluble products by either staphylococcal nuclease or by DNAase I. At least four types of chromatin structure can be distinguished by our digestion kinetics experiments.

Cell Cycle↗

PubMed1975