PubMed Health⌕ Search

Biomedical subjects

R Mache

Publications and source records attributed to R Mache.

64 records · Page 4Linked to original sources
PubMed1980

Properties and characterization of a spinach chloroplast RNA polymerase isolated from a tanscriptionally active DNA-protein complex.

A chloroplast RNA polymerase has been isolated from a transcriptionally active spinach plastid DNA-protein complex. The properties of the complex and of the reconstituted system have been compared. The crude enzyme is at least sevenfold less active when compared with the complex. RNA synthesis by the reconstituted system is sensitive to high ionic strength and heparin, contrarily to RNA synthesis by the chloroplast DNA-protein complex. On the other hand, rifampicin has no inhibitory effect whatever on the transcriptional system used. The RNA polymerase isolated is more efficient with denatured DNA than with double-stranded DNA and the best template is chloroplast DNA. The crude RNA polymerase isolated migrates in a peak of 11 S in glycerol gradient centrifugation and is located in a single band in non-denaturing polyacrylamide gel electrophoresis. About 30 polypeptides (Mr 15 000--180 000) are part of the complex and only eight of them are found in the RNA polymerase preparation. Only five polypeptides are always present with the same yield. They are probably the subunits of the RNA polymerase. The molecular weight of these subunits ranged from 15 000--69 000, even if the isolation of the enzyme was performed in the presence of protease inhibitors.

Chloroplasts↗
PubMed1979

Post-maturation of the plastid ribosomal RNA in the plant kingdom.

The in vivo fragmentation of the plastid rRNA from plants situated at different places in the evolutionary sclae, with the exception of Algae, was analysed by electrophoresis using fully denaturing conditions. This fragmentation corresponds to an in vivo post-maturation. It exists only in some bacteria and is not random. Five main groups of fragments with the following real molecular weights (Mr) are found in 23 S: ca 0.9 x 10(6); 0.7 x 10(6); 0.45 x 10(6); 0.35 x 10(6) and 0.15 x 10(6). The existence of a large fragment (Mr = 0.9 x 10(6)) corresponds to a primitive type of fragmentation found in some archaic plants. Dicotyledons and several other groups have the same pattern of 23 S fragmentation, often comprising all the fragments mentioned above, whilst Graminaceae (Monocotyledons) constitute a special group with a very predominant 0.35 x 10(6) dalton fragment and the absence of the 0.45 x 10(6) dalton fragment. The plastid 16 S rRNA in all plants studied here has a Mr of 0.54 x 10(6) which is smaller than the 16 S of Escherichia coli taken as reference (0.56 x 10(6) dalton).

Biological Evolution↗
PubMed1979

Transcription activity of a DNA-protein complex isolated from spinach plastids.

A DNA . protein complex of about 150 S is isolated from purified spinach chloroplasts by Sepharose 4B gel filtration. A DNA-dependent RNA polymerase activity is found associated with the complex. This DNA protein complex is able to initiate RNA chains in vitro. The RNA synthesis is more dependent on CTP than other nucleoside triphosphates. 50% of the activity is still present with 0.6 M KCl. The temperature optimum occurs between 30 degrees C and 35 degrees C. Rifampicin and rifamycin SV have no inhibitory effect. TNA products have been characterized by gel filtration and by hybridization with chloroplast DNA (ctDNA). At the beginning of transcription DNA products are linked to the transcription complex and are later detached. The molecular weight of the product ranges between 0.07 X 10(6) and 2 X 10(6). A part of the product (3--4%) has a molecular weight higher than 2 X 10(6). No endogenous RNase activity was present during the molecular weight determinations experiments. Hybridization experiments show that at least 75% of the RNA products are hybridizable with ctDNA and that 40% of these products are composed of chloroplast ribosomal RNA, showing that rDNA is preferentially transcribed.

Chloroplasts↗
PubMed1975

Rifampicin inhibition of the plastid rRNA synthesis of Marchantia polymorpha.

The effect of rifampicin on the synthesis of plastid rRNA in Marchantia polymorpha was studied in vivo. As bacterial rRNA and plastid rRNA have the same electrophoretic mobilities, this study was possible only after a method for inhibiting bacterial contamination was developed. It was established that 91-100% of the rRNA synthesized by cultures of bacteria from Marchantia, after a labelling period of 3 and 9 h by 32-P, is inhibited by 10 mug/ml of rifampicin. The same inhibition was observed when Marchantia was labelled for 3 h in the presence of 10 mug/ml of rifampicin, showing that no plastid rRNA was synthesized under out conditions, but only bacterial RNA. However, when labelling was continued for 9 h two important peaks of rRNA (23 and 19 s) were labelled in the presence of 10 or 20 mug/ml of rifampicin. These peaks are of chlorophastic origin as confirmed by the following facts: the labelling is light-activated; plastids isolated from thalli labelled for 12 h also show these two radioactive peaks. Cytoplasmic rRNA is synthesized under certain conditions. The synthesis of plastid rRNA is inhibited by higher concentrations of rifampicin, a concentration of 250 mug/ml producing at least 75% inhibition. Marchantia, a primitive multicellular plant, differs in this respect from higher plants, which seem to be, in most cases, insensitive to rifampicin

Bacteria↗
PubMedDate not supplied

Transcription of the chloroplast DNA: a review.

The transcription systems of chloroplasts and bacteria share different properties. The genetic material of chloroplasts is organized in the same way as bacterial nucleoids. The regulatory DNA sequences for transcription have a strong homology with their E. coli counterparts and some regulatory mechanisms could be conserved. The RNA polymerase subunits and some transcription factors also share similarities with prokaryotes. However, the chloroplast core-enzyme seems to be synthesized in the cytoplasm from nuclear encoded messages.

Amino Acid Sequence↗