Biochemical evidence of translational infidelity and decreased peptidyltransferase activity by a sarcin/ricin domain mutation of yeast 25S rRNA

A C→U mutation (rdn5) in the conserved sarcin/ricin domain of yeast 25S rRNA has been shown to cause translational suppression and paromomycin resistance. It also separates the killing from the misreading effect of this antibiotic. We confirm these findings and provide in vitro evidence that rdn5 causes a 3-fold increase in translational errors and resistance to paromomycin. The role of this 25S rRNA domain in ribosome's decoding function was further demonstrated when 60S subunits from rdn5 cells were combined with 40S subunits from cells carrying an error-prone mutation in the eukaryotic accuracy center ribosomal protein S23, an homologue of Escherichia coli S12. These hybrids exhibited an error frequency similar to that of rdn5 alone, despite the error-prone mutation in S23. This was accompanied by extreme resistance to paromomycin, unlike the effects of the individual mutations. Furthermore, rdn5 lowers peptidyltransferase activity measured as a second-order rate constant (k(cat)/K(s)) corresponding to the rate of peptide bond formation. This mutation was also found to affect translocation. Elongation factor 2 (EF2)-dependent translocation of Ac-Phe-tRNA from the A- to P-site was achieved at an EF2 concentration 3.5 times lower than in wild type. In conclusion, the sarcin/ricin domain of 25S rRNA influences decoding, peptide bond formation and translocation

Inhibition of Aortic Valve Calcification by Local Delivery of Zoledronic Acid-an Experimental Study

The aim of this study was to evaluate in an experimental model of aortic valve (AV) stenosis the effectiveness of zoledronate on the inhibition of calcification. Sixteen New Zealand rabbits were placed on vitamin D-enriched diet for 3 weeks. All animals underwent PET/CT at baseline and before euthanasia to assess calcification. Thereafter, the AVs of eight animals were treated with local delivery of 500 mu g/l zoledronate. A placebo mixture was administered in the remaining eight animals. Standardized uptake values were corrected for blood pool activity, providing mean tissue to background ratios (TBRmean). In the zoledronate group, there was no progression of AV calcification (TBRmean 1.20 +/- 0.12 vs 1.17 +/- 0.78,p = 0.29), while AV calcification progressed in the placebo group (1.22 +/- 0.15 vs 1.53 +/- 0.23,p = 0.006). Ascending aorta (AA) calcification progressed in both zoledronate and placebo groups. Histology confirmed the results of the PET/CT. Inhibition of AV calcification by local delivery of zoledronate is feasible and effective