RNA-binding proteins impacting on internal initiation of translation.

RNA-binding proteins (RBPs) are pivotal regulators of all the steps of gene expression. RBPs govern gene regulation at the post-transcriptional level by virtue of their capacity to assemble ribonucleoprotein complexes on certain RNA structural elements, both in normal cells and in response to various environmental stresses. A rapid cellular response to stress conditions is triggered at the step of translation initiation. Two basic mechanisms govern translation initiation in eukaryotic mRNAs, the cap-dependent initiation mechanism that operates in most mRNAs, and the internal ribosome entry site (IRES)-dependent mechanism activated under conditions that compromise the general translation pathway. IRES elements are cis-acting RNA sequences that recruit the translation machinery using a cap-independent mechanism often assisted by a subset of translation initiation factors and various RBPs. IRES-dependent initiation appears to use different strategies to recruit the translation machinery depending on the RNA organization of the region and the network of RBPs interacting with the element. In this review we discuss recent advances in understanding the implications of RBPs on IRES-dependent translation initiation.

G3BP1 interacts directly with the FMDV IRES and negatively regulates translation.

RNA-protein interactions play a pivotal role in the function of picornavirus internal ribosome entry site (IRES) elements. Here we analysed the impact of Ras GTPase SH3 domain binding protein 1 (G3BP1) in the IRES activity of foot-and-mouth disease virus (FMDV). We found that G3BP1 interacts directly with three distinct sequences of the IRES element using RNA electrophoretic mobility-shift assays. Analysis of the interaction with domain 5 indicated that the G3BP1 binding-site is placed at the single-stranded region although it allows large sequence heterogeneity and the hairpin located upstream of this region enhances retarded complex formation. In addition, G3BP1 interacts directly with the polypyrimidine tract-binding protein and the translation initiation factor 4B (eIF4B) through the C-terminal region. Moreover, G3BP1 is cleaved during FMDV infection yielding two fragments, Ct-G3BP1 and Nt-G3BP1. Both fragments inhibit cap- and IRES-dependent translation, but the Ct-G3BP1 fragment shows a stronger effect on IRES-dependent translation. Assembly of complexes with G3BP1 results in a significantly reduced local flexibility of the IRES element, consistent with the negative effect of this protein. Our results highlight the IRES-binding capacity of G3BP1 and illustrate its function as a translation inhibitor.

Loading and release of ibuprofen in multi- and monofilament surgical sutures.

The preparation of mono- and multifilament sutures incorporating ibuprofen as an anti-inflammatory agent is considered. Poly(p-dioxanone) monofilament samples can be loaded by a molecular diffusion process using a swelling agent such as dichloromethane. The mechanical properties have been measured and have not shown a significant change for the ibuprofen loaded samples in knot tensile assays. The kinetics of both the loading process and the release in a Sörensen's medium at 37 degrees C have been investigated. Diffusion coefficients have also been estimated from film and slab poly(p-dioxanone) samples containing ibuprofen and their release behavior compared to that shown by monofilaments. Release from a coating copolymer based on lactide, epsilon-caprolactone and trimethylene carbonate (PLA/PCA/PTMC 10/60/30) has also been studied. This coating solubilizes ibuprofen molecules well and can be used for braided sutures or when a rapid dose of ibuprofen is preferred.

Triclosan release from coated polyglycolide threads.

Copolymerization of lactide, epsilon-caprolactone, and trimethylene carbonate is performed. The synthesis is focused on obtaining materials with adequate properties for application as a suture coating that could contain an antimicrobial agent like triclosan. An amorphous character, a low glass transition temperature, a moderate susceptibility to degradation, and a hydrophobic nature are the conditions required for the optimal behavior of this coating. These properties can be attained with a copolymer of composition 10:60:30. Triclosan is added to the surface of polyglycolide threads and its release is studied in different media with high-performance liquid chromatography. The influence of the temperature, the diameter of the thread, the initial concentration of the antibacterial agent, and the applied procedure on the incorporation of triclosan is also evaluated. A total release of triclosan is attained after a few days of exposure to a Dulbecco's based medium, whereas equilibrium concentrations are reached when a Sörensen hydrophilic medium is used. Partition and diffusion coefficients are also estimated.

N-chloroacetyl-beta-alanine.

The beta-alanine residue of the title compound, C(5)H(8)ClNO(3), has a ggt folded conformation, which is mainly stabilized through intermolecular N-H...O=C (amide-acid) and O-H...O=C (acid-amide) hydrogen bonds. In addition, a cis conformation is found for the Cl-CH(2)-C(=O)-NH torsion angle, which is associated with the presence of an intramolecular hydrogen bond.