Almond Skin Extracts and Chlorogenic Acid Delay Chronological Aging and Enhanced Oxidative Stress Response in Yeast

Almond (Prunus dulcis (Mill.) D.A.Webb) is one of the largest nut crops in the world. Recently, phenolic compounds, mostly stored in almond skin, have been associated with much of the health-promoting behavior associated with their intake. The almond skin enriched fraction obtained from cold-pressed oil residues of the endemic Moroccan Beldi ecotypes is particularly rich in chlorogenic acid. In this study, both almond skin extract (AE) and chlorogenic acid (CHL) supplements, similar to traditional positive control resveratrol, significantly increased the chronological life-span of yeast compared to the untreated group. Our results showed that AE and CHL significantly reduced the production of reactive oxygen and nitrogen species (ROS/RNS), most likely due to their ability to maintain mitochondrial function during aging, as indicated by the maintenance of normal mitochondrial membrane potential in treated groups. This may be associated with the observed activation of the anti-oxidative stress response in treated yeast, which results in activation at both gene expression and enzymatic activity levels for SOD2 and SIR2, the latter being an upstream inducer of SOD2 expression. Interestingly, the differential gene expression induction of mitochondrial SOD2 gene at the expense of the cytosolic SOD1 gene confirms the key role of mitochondrial function in this regulation. Furthermore, AE and CHL have contributed to the survival of yeast under UV-C-induced oxidative stress, by reducing the development of ROS/RNS, resulting in a significant reduction in cellular oxidative damage, as evidenced by decreased membrane lipid peroxidation, protein carbonyl content and 8-oxo-guanine formation in DNA. Together, these results demonstrate the interest of AE and CHL as new regulators in the chronological life-span and control of the oxidative stress response of yeast.

Transcriptional Fidelity of Mitochondrial RNA Polymerase RpoTm from Arabidopsis thaliana

Fidelity of RNA synthesis is essential for the faithful transfer of information from DNA to RNA. A comprehensive analysis of the nucleotide selectivity by the mitochondrial RNA polymerase (RNAP) RpoTm, from Arabidopsis thaliana, has been carried out. The kinetic parameters for the incorporation of cognate, noncognate, and oxidized bases have been determined. The results establish high fidelity of mitochondrial transcription resembling those of replicative polymerases in the absence of repair. In addition, RpoTm incorporates oxidized nucleotides with similar efficiency compared with mismatches and is capable of extending the RNA beyond the insertion of the oxidized base. Furthermore, lesion bypass study on RpoTm demonstrates that the enzyme bypasses 8-oxo-guanine by insertion of adenine leading to C to A mutations in RNA. Homology modeling of RpoTm elongation complex allows delineation of the residues necessary for stabilizing the incoming NTP substrate and for posing the template nucleotide residue. Substitution of these residues leads to compromise in the activity of the enzyme corroborating their importance in RNA synthesis. Comparison of the data with T7 RNAPs indicates that low efficiency of misincorporation is a universal strategy used by single-subunit RNAPs for maintaining high fidelity in the absence of proofreading and repair activity in mitochondria.