In vitro selection of RNA lectins: using combinatorial chemistry to interpret ribozyme evolution

BACKGROUND: It has been hypothesized that the fact that both ribosomal RNA and the group I intron can bind to aminoglycoside antibiotics implies that these RNAs are evolutionarily related. This hypothesis requires the assumption that there are relatively few ways for RNA molecules to form aminoglycoside-binding sites. RESULTS: We have used in vitro selection to determine the diversity of aminoglycoside-binding sites that can be formed by RNA molecules. We have generated RNA 'lectins' that can bind aminoglycosides tightly and specifically. Sequence analysis indicates that there are many different ways to form tight and specific aminoglycoside binding sites. These artificially selected binding sites are functionally similar to those that have arisen from natural selection. CONCLUSIONS: Our results suggest that the presence of aminoglycoside-binding sites on RNA molecules may not be a useful trait for determining evolutionary relatedness. Instead, the fact that RNA molecules can bind these 'low molecular-weight effectors' may indicate that natural products such as aminoglycosides have evolved to exploit sequence- and structure-specific recognition of nucleic acids, in much the same way that lexitropsins have been designed by chemists to recognise specific nucleic acid sequences.     

Functional limitations to daily living tasks in the aged: a focus group analysis

We assessed constraints on daily living of 59 healthy, active adults 65-88 years of age in focus group interviews. Individual comments about specific problems were coded along the dimensions of (a) the locus of the problem (motor, visual, auditory, cognitive, external, or health limitations); (b) the activity involved (e.g., transportation, leisure, housekeeping); (c) whether the problem was attributable to task difficulty or the perception of risk; and (d) response to limitations (perseverance, cessation, compensation, or self-improvement). The data provide information about the types of difficulties encountered in everyday activities as well as the way in which individuals respond to such difficulties. Each comment was also coded in terms of whether it was remediable via training, design changes, or some combination of the two. More than half of the problems that were reported had the potential to be improved in some way, thus providing direction for future research in human factors and aging. Actual or potential applications of this research include identifying problems and difficulties that older adults encounter in daily activities such as transportation and leisure; more specifically, determining the degree to which such problems are potentially remediable by human factors solutions. Applications of this research also include understanding the types of systems, products, and technologies that older adults interact with currently, or are interested in learning to use.     

CD95 expression in aged mice infected with tuberculosis

The interaction between CD95 and its ligand is an important homeostatic mechanism that leads to the induction of apoptosis in activated T cells. In view of recent evidence that this pathway might be defective in aged mice, this study investigated CD95 expression on T cells in old mice activated by infection with Mycobacterium tuberculosis. The results of the study do not support the hypothesis that CD95 is poorly expressed on CD4 T cells from old mice; instead, it was found that similar numbers of T cells from young and old mice expressed CD95, with the intensity of expression if anything higher on the cells from the old mice. In addition, the study demonstrated that changes in CD44 and CD45RB expression previously observed in young infected mice proceeded in a similar fashion in old animals and, as would be predicted, that CD95(hi) expression was primarily associated with CD4 T cells expressing the activated CD44(hi) CD45RBhi phenotype.     

Purification and characterization of human topoisomerase I mutants

A system for rapid purification and characterization of eukaryotic topoisomerase-I mutants has been developed. The system utilizes six-histidine tagging of human topoisomerase I expressed in Saccharomyces cerevisiae to enable purification by nickel-affinity chromatography. Virtually homogenous mutant proteins are then tested for their ability to relax supercoiled DNA plasmids and their capacity for binding, cleaving and religating short defined DNA substrates. Relaxation-deficient mutants were obtained by site-directed mutagenesis of selected highly conserved amino acids. The mutants Tyr723Phe (active site mutation), Arg488Gln and Lys532Glu were inert in relaxation of DNA, whereas Lys720Glu showed a 50-fold reduction in specific relaxation activity. Accordingly, only Lys720Glu showed low, but detectable cleavage activity on suicide DNA substrates, uncoupling the cleavage and religation events of topoisomerase I. The relative religation efficiency of Lys720Glu comparable to that of wild-type topoisomerase I, indicating that Lys720 is involved in interactions important for normal DNA cleavage, but not for the religation reaction. All mutants could be cross linked by ultraviolet light to bromo-dUTP-substituted DNA oligonucleotides carrying a topoisomerase-I-binding site, indicating that the deficiency of Tyr723Phe, Arg488Gln and Lys532Glu in DNA relaxation and cleavage is not due to an inability of these mutants to bind DNA non-covalently.     

Disorders of excessive daytime sleepiness--an update

Disorders of excessive daytime sleepiness (EDS) constitute a major health hazard, since impaired alertness may lead to accidents and poor quality of life, and some of them are associated with increased cardiovascular morbidity and mortality. Many disorders of EDS are neurological diseases (e.g. narcolepsy and periodic limb movements in sleep, PLMS). The largest group of disorders causing EDS consists of sleep-related disturbances of breathing, where neuroregulatory mechanisms play a major role in pathophysiology. Many patients with neurodegenerative and neuromuscular diseases suffer from sleep disturbances associated with EDS. Therefore, neurologists must be acquainted with the differential diagnosis of EDS and the major categories of sleep disorders causing it. The present update focuses on major sleep disorders causing EDS, and approaches the topic from the neurologist's perspective. Rather than being an extensive review, this update includes recent data on epidemiology, pathophysiology, diagnosis and treatment of obstructive sleep apnea and related conditions (increased upper airway resistance syndrome, central sleep apnea), as well as of narcolepsy and PLMS. Also included are recent data concerning EDS in neurodegenerative (Alzheimer's disease, Parkinson's disease, multiple system atrophy) and neuromuscular disorders.     

Facilitation of feedback inhibition through blockade of glucocorticoid receptors in the hippocampus

In the present study the effects of intracerebroventricular (i.c.v.) and intrahippocampal administration of corticosteroid antagonists on basal hypothalamic-pituitary-adrenal (HPA) activity around the diurnal peak were compared in male Wistar rats. In two separate experiments the glucocorticoid receptor (GR) antagonist RU 38486 and the mineralocorticoid receptor (MR) antagonist RU 28318 were tested. One hour after GR antagonist injection, significant increases in plasma ACTH and corticosterone levels were observed in the i.c.v. treated rats, when compared to vehicle. In contrast, a significant decrease in ACTH levels, and a slight, but non-significant decrease in corticosterone concentrations were attained one hour after intrahippocampal injection of the GR antagonist. Injection of the MR antagonist, on the other hand, resulted in enhanced ACTH and corticosterone levels irrespective of the site of injection. These findings suggest that negative feedback inhibition at the circadian peak involves hippocampal MRs and extrahippocampal (hypothalamic) GRs. The latter feedback inhibition overrides a positive feedback influence exerted by endogenous corticosteroids through hippocampal GRs.     

Identification of childhood vaccine providers in Maryland

Chronic inflammation seems to play a major role in skin and muscle cell damage in dermatomyositis. Adhesion molecules and their ligands are fundamental in regulating inflammation. We have carried out an immunohistochemical analysis of different activation-inducible adhesion markers in 15 biopsy specimens from dermatomyositis skin lesions. Consistent findings were the increased expression of intercellular adhesion molecule-1 (ICAM-1) on endothelial cells, inflammatory cells and focally grouped keratinocytes in contact with subepidermal inflammatory infiltrates. Immunoreactivity for vascular cell adhesion molecule-1 (VCAM-1) was predominant on endothelial cells of the upper reticular dermis and dermal stellate-shaped cells. E-selectin (endothelial leukocyte adhesion molecule-1) immunoreactivity was less extensive, detected mostly on segments of vessels of the papillary dermis and upper reticular dermis, and sometimes independent of inflammation. This pattern of adhesion molecule expression is similar to that described in other immunemediated dermatoses. The up-regulation of the adhesion molecules appears to play a role in the development and perpetuation of dermatomyositis skin lesions.