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Biomedical subjects

B R Jordan

Publications and source records attributed to B R Jordan.

At least 91 records · Page 5Linked to original sources
PubMed1979

Sequence and secondary structure of Drosophila melanogaster 5.8S and 2S rRNAs and of the processing site between them.

Drosophila melanogaster 5.8S and 2S rRNAs were end-labeled with 32p at either the 5' or 3' end and were sequenced. 5.8S rRNA is 123 nucleotides long and homologous to the 5' part of sequenced 5.8S molecules from other species. 2S rRNA is 30 nucleotides long and homologous to the 3' part of other 5.8S molecules. The 3' end of the 5.8S molecule is able to base-pair with the 5' end of the 2S rRNA to generate a helical region equivalent in position to the "GC-rich hairpin" found in all previously sequenced 5.8S molecules. Probing the structure of the labeled Drosophila 5.8S molecule with S1 nuclease in solution verifies its similarity to other 5.8S rRNAs. The 2S rRNA is shown to form a stable complex with both 5.8S and 26S rRNAs separately and together. 5.8S rRNA can also form either binary or ternary complexes with 2S and 26S rRNA. It is concluded that the 5.8S rRNA in Drosophila melanogaster is very similar both in sequence and structure to other 5.8 rRNAs but is split into two pieces, the 2S rRNA being the 3' part. 2S anchors the 5.8S and 26S rRNA. The order of the rRNA coding regions in the ribosomal DNA repeating unit is shown to be 18S - 5.8S - 2S - 26S. Direct sequencing of ribosomal DNA shows that the 5.8S and 2S regions are separated by a 28 nucleotide spacer which is A-T rich and is presumably removed by a specific processing event. A secondary structure model is proposed for the 26S-5.8S ternary complex and for the presumptive precursor molecule.

Animals↗
PubMed1979

alpha-Hydroxylation of newly synthesised fatty acids by a soluble fraction from germinating pea.

A soluble fraction from germinating pea (Pisum sativum) seeds alpha-hydroxylated newly-synthesised fatty acids to form alpha-hydroxypalmitic and alpha-hydroxystearic acids. In contrast to fatty acid synthesis from [14C] malonyl CoA, alpha-hydroxylation was inhibited by exogenous phospholipids. alpha-Hydroxylation was optimal at pH 8, required reduced pyridine nucleotides and was inhibited by EDTA and imidazole.

Fabaceae↗
PubMed1979

Effects of Light and Inhibitors on Glutamate Metabolism in Leaf Discs of Vicia faba L: Sources of ATP for Glutamine Synthesis and Photoregulation of Tricarboxylic Acid Cycle Metabolism.

Metabolism of [(14)C]glutamate was studied in leaf discs of Vicia faba L. in light and in darkness. In white light glutamine was the main labeled product. In the dark label was principally in compounds closely associated with tricarboxylic acid cycle metabolism, predominantly aspartate. Entry of label from glutamate into tricarboxylic acid metabolism appeared to be at least partially by decarboxylation of glutamate to gamma-amino butyric acid, followed by conversion to succinate. 3-(3,4-dichlorophenyl)-1, 1-Dimethylurea inhibited light-enhanced synthesis of glutamine and caused reversion toward the dark pattern of metabolism. Methionine sulfoximine severely inhibited glutamine synthesis and caused accumulation of labeled malate.Monochromatic 650 nanometer light gave similar results to white light. Monochromatic light of 710 nanometers had a much smaller effect on glutamine synthesis but did significantly raise the ratio of labeled malate to aspartate. gamma-Amino [(14)C]butyric acid was metabolized entirely via tricarboxylic acid cycle metabolism in light or dark, and in the light the ratio of labeled malate to aspartate was raised.These results suggest that illuminated leaves metabolize glutamate to glutamine mainly in the chloroplasts. When chloroplastic glutamine synthesis fails to take place, either in darkness or in the presence of inhibitors, glutamate is apparently metabolized outside the chloroplast. Light lowers the NAD(+) to NADH ratio outside the chloroplast, consequently altering the equilibrium of the malate dehydrogenase reaction. Alteration of the malate to aspartate ratio by 710 nanometer light suggests that ATP generated by photosystem I-dependent cyclic photophosphorylation may affect extrachloroplastic NAD(+) to NADH ratios.

Journal Article↗
PubMed1977

Partial enzyme digestion studies on Escherichia coli, Pseudomonas, Chlorella, Drosophila, HeLa and yeast 5S RNAs support a general class of 5S RNA models.

Fox and Woese (1975a) have shown that a model of 5S RNA secondary structure similar to the one originally derived for Chlorella 5S RNA can be generalized with relatively minor variations to all sequenced 5S RNA molecules, i.e. that corresponding base paired regions can be formed at approximately the same positions. We present experimental data in favour of this hypothesis and show that the points at which ribonucleases T1, T2 and pancreatic ribonuclease cleave six different 5S RNA molecules under 'mild' conditions (high ionic strength, low temperature, low RNAase concentration) nearly always fall in the proposed single-stranded regions. We conclude that this model is a good approximation to the conformation of 5S RNA in solution.

Base Sequence↗