Chemical Synthesis of 4-Thiouridine-Containing Substrate Analogues of tRNA:Pseudouridine-55 Synthase: Photocross-Linking Studies

Abstract

For site specific incorporation of 4-thiouridine into oligoribonucleotides a new phosphoramidite is proposed. It makes use of the S-pivaloyloxymethyl group for the protection of the thiol function. This group is easily introduced and removed without modification of the standard protocol for solid phase synthesis of RNA. Three 4-thiouridine-containing oligoribonucleotides (21-mers), corresponding to tRNA minisubstrates of yeast tRNA:pseudouridine-55 synthase (Pus4) were prepared. These 4-thiouridine containing substrates were characterized and used as photoaffinity probe of the enzyme:substrate complex. Irradiation resulted in the specific photocross-linking of these oligoribonucleotides with purified recombinant tRNA:pseudouridine-55 synthase.     

Experimental Studies on Plant Metabolism

Treatment of Ricinus communis seeds with GA accelerated the production of reducing sugars and increased the total carbohydrate content. The effect increased progressively with increasing concentration of GA. — GA treatment also induced an earlier appearance of starch which was shown to be completely absent at the early stages of germination. Furthermore, GA accelerated the conversion of oils into carbohydrates. — Analysis of germinating seeds for their nitrogen content showed that whenever an increase in soluble-N due to GA treatment was detected, there was a decrease in protein-N. Breakdown of protein and formation of soluble-N increased progressively with increase in GA concentration. — GA induced variable changes in the length of the radicles and the hypocotyls, the dry weight and the water content of germinating seeds.     

Experimental and Simulation Studies of Electro-rheology

Abstract

Electro-rheological fluids are colloidal dispersions that, under the influence of an applied electric field, can show a spectacular increase in yield stress and viscosity. Despite many technological roles for fluids with a viscosity that can be controlled electrically, progress at making them commercially viable products has been slow, partly due to a lack of understanding of this phenomenon at the microscopic level. In this report, simulation and experimental data are combined to provide insights into the microscopic origins of this effect. The simulations produce electric field-induced “strings” of particles that span the electrodes, in agreement with the experimental observation, and are responsible for the major enhancements in the viscosity. The field also causes a strong distortion in the first coordination shell of colloidal particles. The combination of shear and electric field produces a long-range microstructure that is periodically forming and decaying, caused by the competing effects of electric field and shear rate. Comparison with experiment reveals that the Electro-rheological effect is driven by the applied field-induced Stokesian diffusion of the solid particles and relies little on the accompanying Brownian motion.     

Experimental Studies of Apospory in Ferns

Apospory in Pteridium aquilinum was found to have several novelfeatures, in particular the rapidity of its occurrence. Outgrowthsfrom detached laminae were detected in as little as 3 days.There was no evidence that failure of co-ordination betweencells, senescence of the sporophytic tissue or unfavourableculture conditions effected the initiation of outgrowths asearlier workers have suggested. The response of Thelypterispalustris was notably slower and more in line with earlier reportsof apospory. Marsilea vestita appeared to be incapable of anyform of aposporous behaviour. The only feature common to all occurrences of apospory in leavesof wild-type ferns is the severance of the lamina from the mainbody of the plant. It is proposed that this may deprive thecells of regulatory substances which maintain the activationof sporophytic genes. The results are also considered in relationto the phase changes in homosporous and heterosporous plantsand the behaviour of fern protoplasts in culture. apospory, ferns, Pteridium aquilinum, Marsilea vestita, Thelypteris palustris