Identification of archaeal proteins that affect the exosome function in vitro

Background  

The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors.     

A new random number generator from permutation groups

We describe a new random number generator, RPGM, which is based on the cryptographic system PGM invented by Magliveras in 1976 and subsequently studied by Magliveras and Surkan [10]. PGM relies on a certain method of machine representation for permutation groups. This method allows for encryption and decryption algorithms based on a space-efficient data structure which is called a logarithmic signature for the group. The efficacy of RPGM is studied by means of an extensive analysis of generated data of 100,000 numbers using the Mathieu groupM ₂₄ in its 5-transitive representation on 24 points.     

E center in silicon has a donor level in the band gap

It has been an accepted fact for more than 40 years that the E center in Si (the group-V impurity--vacancy pair)--one of the most studied defects in semiconductors--has only one energy level in the band gap: namely, the acceptor level at about 0.45 eV below the conduction band. We now demonstrate that it has a second level, situated in the lower half of the band gap at 0.27 eV above the valence band. The existence of this level, having a donor character, is disclosed by a combination of different transient-capacitance techniques and electronic-structure calculations. The finding seriously questions some diffusion-modeling approaches performed in the past.     

High precision delta(17)O isotope measurements of oxygen from silicates and other oxides: method and applications

The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd.     

A NEW FINITE ELEMENT APPROXIMATION OF A STATE-CONSTRAINED OPTIMAL CONTROL PROBLEM

In this paper, we study numerical methods for an optimal control problem with pointwise state constraints. The traditional approaches often need to deal with the deltasingularity in the dual equation, which causes many difficulties in its theoretical analysis and numerical approximation. In our new approach we reformulate the state-constrained optimal control as a constrained minimization problems only involving the state, whose optimality condition is characterized by a fourth order elliptic variational inequality. Then direct numerical algorithms （nonconforming finite element approximation） are proposed for the inequality, and error estimates of the finite element approximation are derived. Numerical experiments illustrate the effectiveness of the new approach.     

ATP-induced lysis of rat parotid secretory granules: possible role of ATP in exocytotic release

Secretory vesicles isolated from a variety of mammalian tissues are known to lyse and thereby release their secretory products when exposed to ATP. This process, which will be termed ATP-induced lysis, has been studied most extensively using adrenal chromaffin-granule preparations. We report here that ATP causes the lysis of a highly purified preparation of rat parotid secretory granules. The rate of granule lysis was measured spectrophotometrically, and ATP-induced lysis was expressed as the increase in the rate of lysis (r = % lysis per min) when ATP was added. This lytic process was characterized with respect to pH, temperature, osmolarity, and the ionic composition of the media. ATP-induced lysis of parotid granules was found to have the following properties in common with the extensively characterized chromaffin-granule process: 1. It is a saturable function of ATP with half-maximal rates observed at 0.5 +/- 0.1 mM ATP. 2. It is temperature dependent, eg, r = 6.1 +/- 2.1%/min at 30 degrees C vs 12.2 +/- 2.5%/min at 37 degrees C. 3. It is inhibited in hyperosmotic media, eg, r = 5.3 +/- 0.3%/min at 0.3 OsM vs 0.8 +/- 0.2%/min at 0.4 OsM. 4. It shows a nucleotide preference of ATP = GTP greater than ADP greater than AMP greater than CTP = ITP. 5. It has an anion requirement. The above findings, combined with reports of ATP-induced lysis of cholinergic, insulin, and posterior-pituitary vesicles, imply that ATP-induced lysis may reflect an ATP-dependent property of all secretory vesicles, and as such, this vesicle property could play a similar role in each exocytotic release process. Using a model system, Miller and Racker [22] made a surprising finding that the extent of which liposomes fuse with a black lipid membrane depends on the osmotic gradient across the vesicle membrane. In view of the osmotic dependence of ATP-induced lysis in this and other secretory-vesicle preparations, we postulate that ATP may prime secretory vesicles for fusion with the plasma membrane by inducing and/or maintaining an osmotic gradient across the vesicle membrane.