Metal ions and the stereochemistry of ribozyme reactions

Inversion of configuration at phosphorus during ribozyme-catalyzed cleavage of RNA is usually considered unequivocal proof of in-line attack, but the relevant pseudorotation diagram for formation of the 2('),3(')-cyclic phosphate shows that inversion is not inconsistent with adjacent attack as long as breakdown of the trigonal bipyramid is in-line. For the reaction to occur by adjacent attack, a normally unstable apical oxyanion in the trigonal bipyramidal intermediate would have to be stabilized. Density-functional calculations show that a metal ion such as magnesium could perform this stabilization. We conclude that the possibility of adjacent attack should not be too hastily dismissed in cases where the setup is closer to adjacent than to in-line geometry.     

The electrochemical proton gradient and phenylalanine transport in Escherichia coli irradiated with near-ultraviolet light.

Irradiation of Escherichia coli with near-ultraviolet (near-UV) light diminished the electrochemical proton gradient and the accumulation of L-phenylalanine. Inhibitors known to collapse the proton gradient and the comparison of two techniques measuring the electrical potential substantiated the estimates made. At several fluences (doses), a linear relationship was observed between the phenylalanine gradient and the combined electrical and chemical potentials (the electrochemical proton gradient), suggesting a close coupling between them. However, additional effects of near-UV light on the phenylalanine permease were not discounted. The combined potentials provided sufficient energy for the observed accumulation of phenylalanine, assuming a proton to amino acid cotransport ratio of 1. An increase in membrane permeability did not contribute to the loss of phenylalanine transport, as shown by an increase in the rate and extent of alpha-methylglucoside uptake.     

Catabolism of thymidine during the lymphocyte cell cycle

Concanavalin A-stimulated lymphocytes degrade thymidine to β-aminoisobutyric acid. Thymidine-catabolizing enzymes are active in the cells during G1, G2 and mitosis, but activity falls to very low levels just prior to the onset of S and remains low throughout the S period. The data suggest that cell pools of thymidine are regulated by degradation.     

Lactational competence and involution of the mouse mammary gland require plasminogen

Urokinase-type plasminogen activator expression is induced in the mouse mammary gland during development and post-lactational involution. We now show that primiparous plasminogen-deficient (Plg(-/-)) mice have seriously compromised mammary gland development and involution. All mammary glands were underdeveloped and one-quarter of the mice failed to lactate. Although the glands from lactating Plg(-/-) mice were initially smaller, they failed to involute after weaning, and in most cases they failed to support a second litter. Alveolar regression was markedly reduced and a fibrotic stroma accumulated in Plg(-/-) mice. Nevertheless, urokinase and matrix metalloproteinases (MMPs) were upregulated normally in involuting glands of Plg(-/-) mice, and fibrin did not accumulate in the glands. Heterozygous Plg(+/-) mice exhibited haploinsufficiency, with a definite, but less severe mammary phenotype. These data demonstrate a critical, dose-dependent requirement for Plg in lactational differentiation and mammary gland remodeling during involution.     

Microarray,SAGE and their applications to cardiovascular diseases

The wealth of DNA data generated by the human genome project coupling with recently invented high-throughput gene expression profiling techniques has dramatically sped up the process for biomedical researchers on elucidating the role of genes in human diseases. One powerful method to reveal insight into gene functions is the systematic analysis of gene expression. Two popular high-throughput gene expression technologies, microarray and Serial Analysis of Gene Expression (SAGE) are capable of producing large amounts of gene expression data with the potential of providing novel insights into fundamental disease processes, especially complex syndromes such as cardiovascular disease, whose etiologies are due to multiple genetic factors and their interplay with the environment. Microarray and SAGE have already been used to examine gene expression patterns of cell-culture, animal and human tissues models of cardiovascular diseases. In this review, we will first give a brief introduction of microarray and SAGE