Head swivel on the ribosome facilitates translocation by means of intra-subunit tRNA hybrid sites

The elongation cycle of protein synthesis involves the delivery of aminoacyl-transfer RNAs to the aminoacyl-tRNA-binding site (A?site) of the ribosome, followed by peptide-bond formation and translocation of the tRNAs through the ribosome to reopen the A?site. The translocation reaction is catalysed by elongation factor G (EF-G) in a GTP-dependent manner. Despite the availability of structures of various EF-G-ribosome complexes, the precise mechanism by which tRNAs move through the ribosome still remains unclear. Here we use multiparticle cryoelectron microscopy analysis to resolve two previously unseen subpopulations within Thermus thermophilus EF-G-ribosome complexes at subnanometre resolution, one of them with a partly translocated tRNA. Comparison of these substates reveals that translocation of tRNA on the 30S subunit parallels the swivelling of the 30S head and is coupled to unratcheting of the 30S body. Because the tRNA maintains contact with the peptidyl-tRNA-binding site (P?site) on the 30S head and simultaneously establishes interaction with the exit site (E?site) on the 30S platform, a novel intra-subunit 'pe/E' hybrid state is formed. This state is stabilized by domain?IV of EF-G, which interacts with the swivelled 30S-head conformation. These findings provide direct structural and mechanistic insight into the 'missing link' in terms of tRNA intermediates involved in the universally conserved translocation process.     

Induction of the synthesis of thymidine kinase by aldosterone in the kidney of the immature male rat

Thymidine kinase activity was studied in kidneys from immature male rats after administration of aldosterone. Kinetic studies showed that the enzyme activity reached its maximum level 24 h after aldosterone injection. That increase was specific for aldosterone and could be related to the synthesis of new molecules of enzyme.     

Phosphoribomutase- und 5-Phosphoriboisomerase-Aktivität in isolierten Zellkernen

Summary The existence of phosphoribomutase and 5-phosphoriboisomerase has been demonstrated in isolated cellular nuclei from rat liver and swine kidney. Phosphoribomutase has been shown to require Mg-ions for optimal activity.     

International equity flows and the predictability of US stock returns

We examined the link between international equity flows and US stock returns. Based on the results of tests of in‐sample and out‐of‐sample predictability of stock returns, we found evidence of a strong positive (negative) link between international equity flows and contemporaneous (one‐month‐ahead) stock returns. Our results also indicate that an investor, in real time, could have used information on the link between international equity flows and one‐month‐ahead stock returns to improve the performance of simple trading rules. Copyright © 2007 John Wiley & Sons, Ltd.     

Fractal morphology, imaging and mass spectrometry of single aerosol particles in flight

The morphology of micrometre-size particulate matter is of critical importance in fields ranging from toxicology to climate science, yet these properties are surprisingly difficult to measure in the particles' native environment. Electron microscopy requires collection of particles on a substrate; visible light scattering provides insufficient resolution; and X-ray synchrotron studies have been limited to ensembles of particles. Here we demonstrate an in situ method for imaging individual sub-micrometre particles to nanometre resolution in their native environment, using intense, coherent X-ray pulses from the Linac Coherent Light Source free-electron laser. We introduced individual aerosol particles into the pulsed X-ray beam, which is sufficiently intense that diffraction from individual particles can be measured for morphological analysis. At the same time, ion fragments ejected from the beam were analysed using mass spectrometry, to determine the composition of single aerosol particles. Our results show the extent of internal dilation symmetry of individual soot particles subject to non-equilibrium aggregation, and the surprisingly large variability in their fractal dimensions. More broadly, our methods can be extended to resolve both static and dynamic morphology of general ensembles of disordered particles. Such general morphology has implications in topics such as solvent accessibilities in proteins, vibrational energy transfer by the hydrodynamic interaction of amino acids, and large-scale production of nanoscale structures by flame synthesis.     

Gene structure and function of the 2'-5'-oligoadenylate synthetase family

2'-5'-Oligoadenylate synthetase was among the first interferon-induced antiviral enzymes to be discovered. This family of enzymes plays an important role in the mechanisms of action of interferon antiviral activity, but is also involved in other cellular processes such as apoptosis and growth control. We have reviewed the function and genomic structure of this class of at least nine proteins. By studying the recently available data in the human genome database and the human Expressed Sequence Tag database, we have been able to build a comprehensive picture of the 2'-5'-oligoadenylate synthetase gene family and its precise location on chromosome 12. Chromosomal localization as well as the intron/exon structure of all four genes has been established and an overview of the splice variant forms of the 2'-5'-oligoadenylate synthetases arising from expression of the four genes is presented. Alignments of the human 2'-5'-oligoadenylate synthetase sequences with non-human 2'-5'-oligoadenylate synthetase sequences suggest that the exon structure and several amino acid sequence motifs have been conserved during evolution.