Recognition of small interfering RNA by a viral suppressor of RNA silencing

RNA silencing (also known as RNA interference) is a conserved biological response to double-stranded RNA that regulates gene expression, and has evolved in plants as a defence against viruses. The response is mediated by small interfering RNAs (siRNAs), which guide the sequence-specific degradation of cognate messenger RNAs. As a counter-defence, many viruses encode proteins that specifically inhibit the silencing machinery. The p19 protein from the tombusvirus is such a viral suppressor of RNA silencing and has been shown to bind specifically to siRNA. Here, we report the 1.85-A crystal structure of p19 bound to a 21-nucleotide siRNA, where the 19-base-pair RNA duplex is cradled within the concave face of a continuous eight-stranded beta-sheet, formed across the p19 homodimer interface. Direct and water-mediated intermolecular contacts are restricted to the backbone phosphates and sugar 2'-OH groups, consistent with sequence-independent p19-siRNA recognition. Two alpha-helical 'reading heads' project from opposite ends of the p19 homodimer and position pairs of tryptophans for stacking over the terminal base pairs, thereby measuring and bracketing both ends of the siRNA duplex. Our structure provides an illustration of siRNA sequestering by a viral protein.     

T cell and T cell subset determination in normal peripheral blood: Comparison of the indirect immunofluorescence and lymphocytotoxicity techniques

Summary We compared a simple complement-dependent lymphocytotoxicity test with a widely used indirect immunofluorescence procedure to enumerate total T, T helper, and T suppressor lymphocytes in normal blood samples. Results with the two techniques were closely similar.     

Mutations in a Sar1 GTPase of COPII vesicles are associated with lipid absorption disorders

Dietary fat is an important source of nutrition. Here we identify eight mutations in SARA2 that are associated with three severe disorders of fat malabsorption. The Sar1 family of proteins initiates the intracellular transport of proteins in COPII (coat protein)-coated vesicles. Our data suggest that chylomicrons, which vastly exceed the size of typical COPII vesicles, are selectively recruited by the COPII machinery for transport through the secretory pathways of the cell.     

SPG20 is mutated in Troyer syndrome,an hereditary spastic paraplegia

Troyer syndrome (TRS) is an autosomal recessive complicated hereditary spastic paraplegia (HSP) that occurs with high frequency in the Old Order Amish. We report mapping of the TRS locus to chromosome 13q12.3 and identify a frameshift mutation in SPG20, encoding spartin. Comparative sequence analysis indicates that spartin shares similarity with molecules involved in endosomal trafficking and with spastin, a molecule implicated in microtubule interaction that is commonly mutated in HSP.     

Ethanol influence on insulin secretion from isolated rat islets

This study was done to delineate the role of alpha- and beta-adrenergic receptors and cyclic AMP in the mechanism of ethanol effects on insulin release from isolated islets. Rats were given an alpha-adrenergic blocker, phentolamine, or a beta-adrenergic blocker, propranolol. In addition, ethanol 1 g/kg was given intragastrically 1 h prior to sacrifice. Glucose mediated insulin release from isolated islets was enhanced by phentolamine and decreased by propranolol. Ethanol treatment inhibited glucose-induced insulin release from isolated islets of control rats as well as those given phentolamine and/or propranolol. Insulin release from isolated islets in response to dibutyryl-cyclic AMP was attenuated by ethanol. Theophylline enhanced glucose mediated insulin release from control islets but ethanol treatment produced a significant inhibition of insulin response. The data suggest that the site of action of the deleterious effects of ethanol on insulin release from isolated islets in rat does not involve adrenergic system and cyclic AMP.     

Some aspects of the hydrolysis of phosphomonoesters by homogenates of growing and regressing mesonephroi in chick embryos

Résumé L'activité de la phosphatase acide envers le-glycérophosphate et le phénylphosphate a été comparée sous des conditions variées afin de constater si ces deux actions reflètent celle de molécules enzymatiques pareilles ou différentes pendant la croissance et la régression du mésonéphros chez l'embryon de poulet. Pour élucider cette question, on a étudié les effets de la température au pH 5, et du versène, et l'influence d'un substratum sur l'hydrolyse. Les résultats de ces recherches indiquent que la même enzyme pourrait être responsable de l'hydrolyse de ces 2 substrats.

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This investigation was supported by NIH Training Grant No. HD-00012.