Demethylation of Methylmercury in Bird, Fish, and Earthworm.

Toxicity of methylmercury (MeHg) to wildlife and humans results from its binding to cysteine residues of proteins, forming MeHg-cysteinate (MeHgCys) complexes that hinder biological functions. MeHgCys complexes can be detoxified , yet how this occurs is unknown. We report that MeHgCys complexes are transformed into selenocysteinate [Hg(Sec)] complexes in multiple animals from two phyla (a waterbird, freshwater fish, and earthworms) sampled in different geographical areas and contaminated by different Hg sources.

N4-methylation of cytosine drastically favors the formation of (6-4) photoproducts in a TCG context.

Methylation of cytosine is a common biological process both in prokaryotic and eukaryotic cells. In addition to 5-methylcytosine (5mC), some bacterial species contain in their genome N(4) -methylcytosine (N4mC). Methylation at C5 has been shown to enhance the formation of pyrimidine dimeric photoproducts but nothing is known of the effect of N4 methylation on UV-induced DNA damage.

Contribution of cytosine-containing cyclobutane dimers to DNA damage produced by photosensitized triplet-triplet energy transfer.

Mutagenic cyclobutane pyrimidine dimers (CPDs) can be induced in DNA through either direct excitation or photosensitized triplet-triplet energy transfer (TTET). In the latter pathway, thymines are expected to receive the excitation energy from the photosensitizer and react with adjacent pyrimidines. By using state-of-the art analytical tools, we provide herein additional information on the formation of cytosine-containing CPDs.