RNA-catalysed nucleotide synthesis

The 'RNA world' hypothesis proposes that early life developed by making use of RNA molecules, rather than proteins, to catalyse the synthesis of important biological molecules. It is thought, however, that the nucleotides constituting RNA were scarce on early Earth. RNA-based life must therefore have acquired the ability to synthesize RNA nucleotides from simpler and more readily available precursors, such as sugars and bases. Plausible prebiotic synthesis routes have been proposed for sugars, sugar phosphates and the four RNA bases, but the coupling of these molecules into nucleotides, specifically pyrimidine nucleotides, poses a challenge to the RNA world hypothesis. Here we report the application of in vitro selection to isolate RNA molecules that catalyse the synthesis of a pyrimidine nucleotide at their 3' terminus. The finding that RNA can catalyse this type of reaction, which is modelled after pyrimidine synthesis in contemporary metabolism, supports the idea of an RNA world that included nucleotide synthesis and other metabolic pathways mediated by ribozymes.     

Bücherschau

Ohne Zusammenfassung VDI     

Creep and Creep Recovery Response of Load Cells Tested According to U.S. and International Evaluation Procedures

The 60 min creep data from National Type Evaluation Procedure (NTEP) tests performed at the National Institute of Standards and Technology (NIST) on 65 load cells have been analyzed in order to compare their creep and creep recovery responses, and to compare the 60 min creep with creep over shorter time periods. To facilitate this comparison the data were fitted to a multiple-term exponential equation, which adequately describes the creep and creep recovery responses of load cells. The use of such a curve fit reduces the effect of the random error in the indicator readings on the calculated values of the load cell creep. Examination of the fitted curves show that the creep recovery responses, after inversion by a change in sign, are generally similar in shape to the creep response, but smaller in magnitude. The average ratio of the absolute value of the maximum creep recovery to the maximum creep is 0.86; however, no reliable correlation between creep and creep recovery can be drawn from the data. The fitted curves were also used to compare the 60 min creep of the NTEP analysis with the 30 min creep and other parameters calculated according to the Organization Internationale de Métrologie Légale (OIML) R 60 analysis. The average ratio of the 30 min creep value to the 60 min value is 0.84. The OIML class C creep tolerance is less than 0.5 of the NTEP tolerance for classes III and III L.     

Talking about time: Effects of temporal planning and time awareness norms on group coordination and performance.

Planning is often central to effective coordination and task performance in work groups. Although planning pertains to efforts aimed at establishing objectives, generating subtasks, and creating role or task assignments, it also encompasses discussions about time and temporal issues. This article highlights the importance of temporal planning in groups, especially as it relates to effective coordination and task performance. Specifically, the results of a survey study of 48 self-managing project groups revealed that higher levels of initial temporal planning contributed to the formation of group norms that emphasize awareness of and attention to time. These time awareness norms were found to mediate the effect of temporal planning on coordination and task performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

1H NMR studies of the high-affinity Rev binding site of the Rev responsive element of HIV-1 mRNA: base pairing in the core binding element

1H NMR studies of a 30-nucleotide RNA oligonucleotide (RBE3), which contains a high-affinity binding site for Rev of the HIV-1 Rev responsive element (RRE), two derivatives of RBE3 (RBE3AA and RBE3-A), and the complex of RBE3 with peptides derived from the RNA binding domain of HIV-1 Rev, are presented. The high-affinity binding site of the RRE consists of an asymmetric internal loop and surrounding Watson-Crick base pairs. In the wild-type RRE, one of the stems is closed by a loop; this is replaced in REB3 by the stable UUCG tetraloop. NOE data suggest that the internal loop of the free RNA contains structural features that have been predicted on the basis of in vitro selection experiments [Bartel, D.P., et al. (1991) Cell 67, 529-536]. The structural features include a Gsyn.Ganti base pair, a Ganti.Aanti base pair, and a looped out U. When the Rev peptide is bound to the RNA, the base pairs in the internal loop appear to be stabilized, although the RNA chemical shifts indicate that the RNA conformation undergoes some changes when bound by Rev peptide.     

A technique for eliminating the undesirable effect of enhanced anodic corrosion of installations connected to anodically protected equipment

Two techniques for eliminating the unsiderable effect of anodic protection on installations connected to the protected equipment were tested. Model measurements were carried out in a 50% solution of sulfuric acid at 20°C with a type FeCr 18 Ni9 Ti stainless steel under potentiostatic conditions. The use of an insulating section in the critical range of potentials in the case of tubing passivation does not fully eliminate the increased corrosion due to anodic protection of a major piece of equipment. However, the undesirable effect can be eliminated entirely by installing secondary electrodes which pass electric current so as to set up the desired drop of potential.