Dispersed repeats and structural reorganization in subclover chloroplast DNA

The plastid genome from subclover, Trifolium subterraneum, is unusual in a variety of respects, compared with other land-plant chloroplast DNAs. Gene mapping of subclover chloroplast DNA reveals major structural reorganization of the genome. Ten clusters of genes are rearranged in both order and orientation. Eight large inversions are sufficient to explain this reorganization; however, the actual evolutionary changes may have been more complex. For example, a fine-scale analysis of a set of ribosomal protein genes reveals the occurrence of insertions, deletions, and transpositions. Associated with this unusually unstable genome are two structural features potentially involved in the rearrangements. A dispersed family of repeats, with each element about 1 kb in length, is present in at least six copies. A survey of a wide taxonomic range of species indicates that these elements are unique to the chloroplast DNAs of subclover and two closely related species. Several of the repeated elements are associated with genomic rearrangements, and one repeat is inserted within a normally highly conserved series of genes. This set of dispersed repeats may be the first family of transposable elements found in any organelle genome. In addition, the subclover genome is much larger than those in other closely related legumes, even when one takes into account the presence of the repeated elements. Some of the extra DNA has no sequence similarity to other chloroplast genomes and may represent insertion of DNA from another genome. These unusual features are not found in the structurally stable chloroplast genomes of other vascular plants and may, therefore, be implicated in the rapid and major reorganization of the chloroplast DNA in subclover.     

Cardiovascular control in diabetes mellitus.

Heart rate variability and the changes in heart rate and blood pressure which occur on standing were measured in 21 diabetics. These simple measures distinguished four groups of patients, with loss of parasympathetic activity being commoner than loss of sympathetic activity.     

La dormance embryonnaire chez Taxus baccata: Influence de la composition du milieu liquide sur I'induction de la germination Par

Embryo dormancy of Taxus baccata var. fastigiata is eliminated when cultured continuously in nutritive liquid medium. An equivalent percentage of germination is obtained when the embryos are transferred to agar medium after 8 days of liquid culture. There is no morphological development of the embryo during the period in the liquid medium. But we have ascertained that water-soluble germination inhibitors present in the embryo are leached out into the medium, permitting germination. Germination is totally absent when the embryos are cultured continuously in distilled water, alone or with minerals; incidental in sucrose solution; and maximal when the medium contains sucrose and Ca²⁺ or K⁺ ions. The extent of germination on agar medium depends upon the composition of the liquid medium in which the embryos are cultured for the initial 8 days. But this preliminary culture in the liquid medium does not always remove the endogenous inhibitors, irrespective of its composition. This can be achieved only in the presence of sucrose; and this process can be made more effective by the addition of Ca²⁺ ions.     

Regulation of two aspartokinases in Bacillus subtilis

When grown on minimal glucose medium, transformable Bacillus subtilis strains contained two distinct aspartokinases (ATP:l-aspartate 4-phosphotransferase, EC 2.7.2.4). One of these enzymes was inhibited by l-lysine (Lys), whereas the other was insensitive to inhibition but was activated by l-leucine. None of the other amino acids tested had any effect, and the addition of l-threonine did not enhance the inhibition by Lys, in contrast to the concerted inhibition observed for other bacilli. At the end of exponential growth, the Lys-sensitive aspartokinase activity decreased, whereas the Lys-insensitive activity remained relatively constant throughout the stationary phase. The two activities were separated by (NH(4))(2)SO(4) fractionation and Sephadex G-200 chromatography. Growth in the presence of Lys reduced the specific activity of aspartokinase by about 50% and eliminated the inhibition by Lys. In extracts of these cells, only Lys-insensitive activity was found upon (NH(4))(2)SO(4) fractionation and Sephadex G-200 chromatography. Lys apparently repressed the synthesis of the Lys-sensitive enzyme.     

Facilitated Penetration of Amanitin—Albumin Conjugates into Hepatocytes after Coupling with Fluorescein

α-AMANITIN, a cyclic peptide of the toadstool Amanita phalloides^1,2, causes necrosis of liver and kidney cells, the first morphological lesions occurring in the nuclei^3,4. It acts by binding to RNA polymerase in eukaryotic .cells and inhibiting the enzyme^5–9. The hepatotoxicity of amanitin increases several times when it is conjugated to albumin, probably because of a slower rate of elimination of the toxin through the glomeruli^4,10. It is unlikely that the amanitin-albumin conjugate enters the hepatocyte by a mechanism involving its albumin moiety; it was therefore suggested¹¹ that penetration of the liver cells is consequent on binding of the amanitin group to the carrier involved in transport of this peptide. This led us to consider more generally the facilitation of penetration into cells by large molecules by means of binding to another molecule for which a carrier exists on the cell membrane^12,13.     

Specific binding of the C-peptide of proinsulin to cultured B-cells from a transplantable rat islet cell tumor

Specific binding of the C-peptide of proinsulin was evaluated using a transplantable NEDH rat islet cell tumour predominantly composed of insulin-secreting B-cells. Cultured tumour B-cells exhibited greater than 90% viability assessed by trypan blue exclusion, and retained the ability to form tumours with accompanying hypoglycaemia and hyperinsulinaemia after reimplantation. During binding experiments with synthetic rat C-peptide I and iodinated tyrosylated rat C-peptide I, turnout B-cells exhibited 54±6% specific binding. Displacement of tracer increased with increasing concentrations of unlabelled rat C-peptide I (0.25–1,000 ng/ml), and the specificity of binding was substantiated by reduced displacement with human C-peptide. Scatchard analysis of specific C-peptide binding revealed a curvilinear plot with upward concavity. The demonstration of specific C-peptide binding to insulin-secreting B-cells provides evidence for a physiological role of proinsulin C-peptide.     

Trial of early nifedipine in acute myocardial infarction: the Trent study.

Over 30 months 9292 consecutive patients admitted to nine coronary care units with suspected myocardial infarction were considered for admission to a randomised double blind study comparing the effect on mortality of nifedipine 10 mg four times a day with that of placebo. Among the 4801 patients excluded from the study the overall one month fatality rate was 18.2% and the one month fatality rate in those with definite myocardial infarction 26.8%. A total of 4491 patients fulfilled the entry criteria and were randomly allocated to nifedipine or placebo immediately after assessment in the coronary care unit. Roughly 64% of patients in both treatment groups sustained an acute myocardial infarction. The overall one month fatality rates were 6.3% in the placebo treated group and 6.7% in the nifedipine treated group. Most of the deaths occurred in patients with an in hospital diagnosis of myocardial infarction, and their one month fatality rates were 9.3% for the placebo group and 10.2% for the nifedipine group. These differences were not statistically significant. Subgroup analysis also did not suggest any particular group of patients with suspected acute myocardial infarction who might benefit from early nifedipine treatment in the dose studied.     

Studies of the fatty acid composition and membrane microviscosity in Salmonella typhimurium TA98

When the mutagen tester bacterial strain Salmonella typhimurium TA 98 was grown at different temperatures, we found that the unsaturated fatty acid composition increased at the lower growth temperatures. Membrane microviscosity, as assessed with spin-probe fatty acids using electron spin resonance, decreased as the unsaturated fatty acid content increased. These findings are of importance in understanding our recent observation that the mutagenic response of these bacteria was increased when they were grown at 27 degrees C vs. 37 degrees C, and indicate that membrane properties may play an important role in the sequence of events leading to mutagenesis.