Molecular modelling of the GIR1 branching ribozyme gives new insight into evolution of structurally related ribozymes

Twin-ribozyme introns contain a branching ribozyme (GIR1) followed by a homing endonuclease (HE) encoding sequence embedded in a peripheral domain of a group I splicing ribozyme (GIR2). GIR1 catalyses the formation of a lariat with 3 nt in the loop, which caps the HE mRNA. GIR1 is structurally related to group I ribozymes raising the question about how two closely related ribozymes can carry out very different reactions. Modelling of GIR1 based on new biochemical and mutational data shows an extended substrate domain containing a GoU pair distinct from the nucleophilic residue that dock onto a catalytic core showing a different topology from that of group I ribozymes. The differences include a core J8/7 region that has been reduced and is complemented by residues from the pre-lariat fold. These findings provide the basis for an evolutionary mechanism that accounts for the change from group I splicing ribozyme to the branching GIR1 architecture. Such an evolutionary mechanism can be applied to other large RNAs such as the ribonuclease P

Computer-Aided Systems and Communities: Mechanisms for Organizational Learning in Distributed Environments

This paper examines the role of computer-aided systems (CAS) for enhancing organizational learning in distributed environments. The basic research questions are: how do features of CAS enhance organizational learning, and how does organizational context influence the role of CAS in organizational learning? The theoretical framework focuses on the decision to contribute and adopt knowledge in distributed environments. Specifically, we investigate the intersections between the features of CAS and inhibitors to contributing or adopting knowledge, in the light of different organizational context variables. Two cases of information environments for knowledge sharing are examined: a formal electronic library system and an informal community that uses a variety of communication technologies. The cases are used to illustrate how the intersection between CAS features and the decisions to adopt and contribute enhance or inhibit knowledge sharing.</p

Supercritical CO2 mediated incorporation of Pd onto templated carbons: a route to optimizing the Pd particle size and hydrogen uptake density.

Palladium nanoparticles are deposited onto zeolite template carbon (ZTC) via supercritical CO2 (scCO2) mediated hydrogenation of a CO2-phillic transition metal precursor. The supercritical fluid (SCF) mediated metal incorporation approach enabled the decoration of ZTC with 0.2-2.0 wt % of well-dispersed Pd nanoparticles of size 2-5 nm. The resulting Pd-doped ZTCs exhibit enhanced hydrogen uptake and storage density. The ZTC (with surface area of 2046 m(2)/g) had a hydrogen storage capacity (at 77 K and 20 bar) of 4.9 wt %, while the Pd-ZTCs had uptake of 4.7-5.3 wt % despite a surface area in the range 1390-1858 m(2)/g. The Pd-ZTCs thus exhibit enhanced hydrogen storage density (14.3-18.3 μmol H2/m(2)), which is much higher than that of Pd-free ZTC (12.0 μmol H2/m(2)). The hydrogen isosteric heat of adsorption (Qst) was found to be higher for the Pd-doped carbons (6.7 kJ/mol) compared to the parent ZTC (5.3 kJ/mol). The deposition of small amounts of Pd (up to 2 wt %) along with well-dispersed Pd nanoparticles of size of 2-5 nm is essential for the enhancement of hydrogen uptake and illustrates the importance of optimizing the balance between metal loading/particle size and surface area to achieve the best metal/porous carbon composite for enhanced hydrogen uptake