Antimony is a toxic metalloid with poorly understood mechanisms of toxicity and uncertain carcinogenic properties. By using a combination of genetic, biochemical and DNA damage assays, we investigated the genotoxic potential of trivalent antimony in the model organism Saccharomyces cerevisiae. We found that low doses of Sb(III) generate various forms of DNA damage including replication and topoisomerase I-dependent DNA lesions as well as oxidative stress and replication-independent DNA breaks accompanied by activation of DNA damage checkpoints and formation of recombination repair centers. At higher concentrations of Sb(III), moderately increased oxidative DNA damage is also observed. Consistently, base excision, DNA damage tolerance and homologous recombination repair pathways contribute to Sb(III) tolerance. In addition, we provided evidence suggesting that Sb(III) causes telomere dysfunction. Finally, we showed that Sb(III) negatively effects repair of double-strand DNA breaks and distorts actin and microtubule cytoskeleton. In sum, our results indicate that Sb(III) exhibits a significant genotoxic activity in budding yeast.

DNA damage tolerance and homologous recombination pathways function to bypass replication-blocking lesions and ensure completion of DNA replication. However, inappropriate activation of these pathways may lead to increased mutagenesis or formation of deleterious recombination intermediates, often leading to cell death or cancer formation in higher organisms. Post-translational modifications of PCNA regulate the choice of repair pathways at replication forks. Its monoubiquitination favors translesion synthesis, while polyubiquitination stimulates template switching. Srs2 helicase binds to small ubiquitin-related modifier (SUMO)-modified PCNA to suppress a subset of Rad51-dependent homologous recombination. Conversely, SUMOylation of Srs2 attenuates its interaction with PCNA Sgs1 helicase and Mus81 endonuclease are crucial for disentanglement of repair intermediates at the replication fork. Deletion of both genes is lethal and can be rescued by inactivation of Rad51-dependent homologous recombination. Here we show that Uls1, a member of the Swi2/Snf2 family of ATPases and a SUMO-targeted ubiquitin ligase, physically interacts with both PCNA and Srs2, and promotes Srs2 binding to PCNA by downregulating Srs2-SUMO levels at replication forks. We also identify deletion of as a suppressor of ΔΔ synthetic lethality and hypothesize that Δ mutation results in a partial inactivation of the homologous recombination pathway, detrimental in cells devoid of both Sgs1 and Mus81 We thus propose that Uls1 contributes to the pathway where intermediates generated at replication forks are dismantled by Srs2 bound to SUMO-PCNA. Upon deletion, accumulating Srs2-SUMO-unable to bind PCNA-takes part in an alternative PCNA-independent recombination repair salvage pathway(s).

Arsenic is an ubiquitous element present in the environment either through geological or anthropogenic activities. Millions of people all over the world are exposed to arsenic mainly via air, drinking water and food sources, which results in higher incidence of cancer. Several mechanisms by which arsenic compounds induce tumorigenesis have been proposed. Arsenic mediates its toxicity by generating oxidative stress, inducing protein misfolding, promoting genotoxicity, hampering DNA repair and disrupting signal transduction. Thus, all organisms have developed multiple pathways for arsenic detoxification. In this article, we review recent advances in the understanding of arsenic toxicity and its transport routes in prokaryotes and eukaryotes, including a dual role of aquaglyceroporins in the uptake and efflux, active transport out of the cell via secondary ion pumps and sequestration of metalloid-thiol conjugates into vacuoles by primary ABC transporters. We believe that such studies are of high importance due to the increasing usage of arsenic-based drugs in the treatment of certain types of cancer and diseases caused by protozoan parasites as well as for the development of bio-and phytoremediation strategies for metalloid-polluted areas. 1. Introduction. 2. The chemical properties and the presence of arsenic in the environment. 3. Pathways for arsenic uptake. 4. Mechanism of trivalent arsenic toxicity. 4.1. Oxidative stress. 4.2. Arsenic binding to proteins. 4.3. Protein aggregation. 5. Pentavalent arsenic toxicity. 6. Cellular detoxification mechanisms of arsenic compounds. 6.1. ars operons. 6.2. ACR genes. 6.3. Removal of arsenic conjugates by the ABC transporters. 6.4. Bi-directional transport of arsenic. 7. Summary