Subcellular organization of Streptomyces aureofaciens and overproduction of chlortetracycline

Biosynthesis of chlortetracycline is localized differently under low- and high-production conditions (standard low-production strain and its high-production variant). The experimental evidence was based on the assay of anhydrotetracycline oxygenase in subcellular fractions, ultracytochemical localization and electron-probe X-ray microanalysis of the product in the mycelium. Overproduction of chlortetracycline is closely associated with compartmentation of biosynthetic enzymes and with an efficient export of the antibiotic out of the cell.     

Medicago truncatula,a model plant for studying the molecular genetics of theRhizobium-legume symbiosis

Medicago truncatula has all the characteristics required for a concerted analysis of nitrogen-fixing symbiosis withRhizobium using the tools of molecular biology, cellular biology and genetics.M. truncatula is a diploid and autogamous plant has a relatively small genome, and preliminary molecular analysis suggests that allelic heterozygosity is minimal compared with the cross-fertilising tetraploid alfalfa (Medicago sativa). TheM. truncatula cultivar Jemalong is nodulated by theRhizobium meliloti strain 2011, which has already served to define many of the bacterial genes involved in symbiosis with alfalfa. A genotype of Jemalong has been identified which can be regenerated after transformation byAgrobacterium, thus allowing the analysis ofin-vitro-modified genes in an homologous transgenic system. Finally, by virtue of the diploid, self-fertilising and genetically homogeneous character ofM. truncatula, it should be relatively straightforward to screen for recessive mutations in symbiotic genes, to carry out genetic analysis, and to construct an RFLP map for this plant.     

Protein stability and electrostatic interactions between solvent exposed charged side chains

To investigate the contribution to protein stability of electrostatic interactions between charged surface residues, we have studied the effect of substituting three negatively charged solvent exposed residues with their side-chain amide analogs in bovine calbindin D9k--a small (Mr 8,500) globular protein of the calmodulin superfamily. The free energy of urea-induced unfolding for the wild-type and seven mutant proteins has been measured. The mutant proteins have increased stability towards unfolding relative to the wild-type. The experimental results correlate reasonably well with theoretically calculated relative free energies of unfolding and show that electrostatic interactions between charges on the surface of a protein can have significant effects on protein stability.     

Variable conservation of nucleolus organizer regions during karyotypic evolution in Microtidae

The location of the nucleolus organizer regions (NORs) was studied in four species of Microtidae (Microtus nivalis, M. cabrerae, M. arvalis, and Arvicola sapidus). The comparative study of these locations shows that some NORs have been conserved despite the chromosome rearrangements that have occurred through karyotypic evolution, while others have been lost. In addition, there are many chromosomes in which NORs seem to have appeared or been lost without apparent relation to the chromosome rearrangements. Some hypotheses regarding these facts are discussed in the text.     

The influence of the athymic mutation nude on the components of the circadian rhythm of activity in mice

The mutation known as nude brings about the lack of a thymus gland in mice. This immunodeficiency akes it possible to graft normally unaccepted, human cancerous tumors onto the mouse. Consequently, this animal is frequently used as a model for evaluating anti-cancer therapies. The effect of this mutation on biological rhythms constitutes a necessary step before using this model for cancer chronotherapy research. We evaluated the circadian and ultradian components of the rest-activity cycle in the following strains of mice: C57BL/6 with homozygous nu/nu, heterozygous nu/+, thymectomised +/+, and sham-operated +/+. The amount of activity was reduced in nu/nu as compared to the other groups. Nonetheless, neither the nude mutation nor thymectomy yielded any notable change in the circadian rhythm of activity.     

Dépistage de l'alcoolisme en médecine familiale: étude pilote de l'association du Michigan Alcoholism Screening Test et le dosage de la gamma-glutamyltransférase sérique.

When used simultaneously, are laboratory and psychosocial methods of screening helpful to detect alcoholism in general practice? To examine this issue, systematic screening with a self-administered Michigan Alcoholism Screening Test and measurement of the plasma gamma-glutamyltransferase level was offered to 435 clients at a family medicine clinic. Whenever a positive finding was obtained the client was free to undergo a more detailed evaluation to confirm the diagnosis. A total of 200 subjects (126 women, 74 men) agreed to undergo screening. The results do not appear to lead to practical consequences among women, in whom no case was identified. In contrast, in the male population a rate of first detection of 9.5% (seven cases) should encourage such screening for alcoholism in family medicine.     

Infectivity inhibition of HIV prototype strains by antibodies directed against a peptide sequence of mycoplasma

Antibodies prepared against a peptide corresponding to the site of cyto-adherence of Mycoplasma genitalium adhesine inhibit or reduce the infectivity of the HIV-1BRU and HIV-2ROD strains of Human Immunodeficiency Virus in lymphoid cells. These results strengthen the hypothesis that some mycoplasmas may play an important part in HIV replication and pathogenicity.     

Binding of brain-derived neurotrophic factor to the nerve growth factor receptor

The neurotrophic proteins BDNF and NGF are related in their primary structures, and both have high- and low-affinity receptors on their responsive neurons. In this study, we investigate the extent to which these receptors can discriminate between BDNF and NGF. We found that a 1000-fold excess of the heterologous ligand is needed to reduce binding to the high-affinity receptor by 50%, but that the same concentrations of BDNF and NGF similarly reduce the binding of either ligand to the low-affinity receptor. Results obtained with cells transfected with the low-affinity NGF receptor gene indicate that these cells bind BDNF, in addition to NGF, whereas cells before transfection do not. These data indicate that the low-affinity NGF receptor is also a low-affinity BDNF receptor and that whatever is conferring high-affinity binding and biological response also considerably reinforces the ability of the low-affinity receptor to discriminate between NGF and BDNF.     

Theoretical studies of protein conformation by means of energy computations

In this review we describe fundamental concepts and applications of conformational energy computations, with emphasis on some recent advances and problems being investigated. The formulation of potential energy functions is described, including the nature of the intramolecular force field, the representation of interactions with the solvent, and considerations of entropy contributions. Approaches to the search for the optimal potential energy are summarized. Examples cited among applications of conformational energy computations include refinement of X-ray crystallographic structures, the use of computations in conjunction with NMR data, prediction of the structures of proteins based on either homology or on other procedures that surmount the multiple-minima problem, the analysis of hierarchical levels of structure and assembly, and interactions in enzyme-substrate complexes.