The DNA polymerase lambda is required for the repair of non-compatible DNA double strand breaks by NHEJ in mammalian cells

DNA polymerase lambda (polλ) is a recently identified DNA polymerase whose cellular function remains elusive. Here we show, that polλ participates at the molecular level in a chromosomal context, in the repair of DNA double strand breaks (DSB) via non-homologous end joining (NHEJ) in mammalian cells. The expression of a catalytically inactive form of polλ (polλDN) decreases the frequency of NHEJ events in response to I-Sce-I-induced DSB whereas inactivated forms of its homologues polβ and polμ do not. Only events requiring DNA end processing before ligation are affected; this defect is associated with large deletions arising in the vicinity of the induced DSB. Furthermore, polλDN-expressing cells exhibit increased sensitization and genomic instability in response to ionizing radiation similar to that of NHEJ-defective cells. Our data support a requirement for polλ in repairing a subset of DSB in genomic DNA, thereby contributing to the maintenance of genetic stability mediated by the NHEJ pathway.     

Iodine transfers in the coastal marine environment: the key role of brown algae and of their vanadium-dependent haloperoxidases

Brown algal kelp species are the most efficient iodine accumulators among all living systems, with an average content of 1.0% of dry weight in Laminaria digitata, representing a ca. 30,000-fold accumulation of this element from seawater. Like other marine macroalgae, kelps are known to emit volatile short-lived organo-iodines, and molecular iodine which are believed to be a main vector of the iodine biogeochemical cycle as well as having a significant impact on atmospheric chemistry. Therefore, radioactive iodine can potentially accumulate in seaweeds and can participate in the biogeochemical cycling of iodine, thereby impacting human health. From a radioecological viewpoint, iodine-129 (129I, half-life of 1.6 x 10(7) years) is one of the most persistent radionuclide released from nuclear facilities into the environment. In this context, the speciation of iodine by seaweeds is of special importance and there is a need to further understand the mechanisms of iodine uptake and emission by kelps. Recent results on the physiological role and biochemistry of the vanadium haloperoxidases of brown algae emphasize the importance of these enzymes in the control of these processes.     

Smc5-Smc6 mediate DNA double-strand-break repair by promoting sister-chromatid recombination

DNA double-strand breaks (DSB) can arise during DNA replication, or after exposure to DNA-damaging agents, and their correct repair is fundamental for cell survival and genomic stability. Here, we show that the Smc5-Smc6 complex is recruited to DSBs de novo to support their repair by homologous recombination between sister chromatids. In addition, we demonstrate that Smc5-Smc6 is necessary to suppress gross chromosomal rearrangements. Our findings show that the Smc5-Smc6 complex is essential for genome stability as it promotes repair of DSBs by error-free sister-chromatid recombination (SCR), thereby suppressing inappropriate non-sister recombination events.     

Quantification of biotin in feed, food, tablets, and premixes using HPLC-MS/MS

Two sensitive and specific methods for quantification of biotin in feed, food, tablets, and premixes based on HPLC-MS/MS have been developed and validated. Depending on sample matrix and biotin content different extraction procedures and HPLC conditions were applied. Key steps in sample preparation were an alkaline extraction or a hydrolysis with sulphuric acid followed by enzymatic digest with papain. For many samples with low biotin content the latter combination of extraction steps was shown to be necessary for an optimal release of biotin from the matrix. The first time synthesis of deuterated biotin for use as internal standard allowed the compensation of losses during sample work-up and ion suppression during HPLC-MS/MS analysis. The new methods are faster than the commonly used microbiological assay using Lactobacillus plantarum. Additionally, they have a higher specificity as results for biotin are based on determination of a chemically defined compound, and not of a biological activity. Quantification is applicable to samples with a biotin content >100 microg/kg. Results obtained with the new methods have been compared with those of the microbiological assay, and were in good agreement.     

Chromatin remodeling: RSC Motors along the DNA

Single-molecule experiments show that the chromatin-remodeling complex RSC, a member of the SNF2 ATPase family, induces formation of a negatively supercoiled DNA loop by active translocation.     

Synthesis and evaluation of NO-release from symmetrically substituted furoxans

A series of symmetrically substituted dibenzoyl furoxans were synthesized and investigated for their potential to release nitric oxide, which plays a key role in the nervous and cardiovascular systems. Cysteine was employed to promote nitric oxide release from furoxan via the formation of an S-nitrosothiol intermediate. Transition metal ion-mediated S-nitrosocysteine decomposition liberates nitric oxide that, in aqueous aerobic solutions, is converted to reactive nitrogen oxide species. The percent nitric oxide released was quantified colorimetrically by the Griess reagent system.