Chemistry: Structure & Mechanisms
DNA is modified by sulphur to form sequence- and stereo-specific phosphorothioate
"SULFUR SURPRISE: This dinucleotide, which occurs naturally in bacterial genomic DNA, possesses a sulfur atom in place of one of the nonbridging oxygen atoms on its phosphate group". Reported by Chemical & Engineering News Oct. 22, 2007, 14.

Wang et al. unpublished data
1. L. Wang, S. Chen, T. Xu, K. Taghizadeh, J. S. Wishnok, X. Zhou, D. You, Z. Deng, Peter C. Dedon (2007). Phosphorothioation of DNA in bacteria by dnd gene clusters, Nature Chem. Bio., 3(11):709-710.
[Abstract] [Full Text] [Supplementary Information]

2. Fritz Eckstein (2007). Phosphorothioation of DNA in bacteria. Nat Chem Biol. 2007 3(11):689-690. [Abstract][Full Text ]
Four key questions about Phosphorothioation of DNA proposed by Fritz Eckstein ?
1. How and why has nature chosen this particular DNA modification?
2. What could be the mechanism of postreplicative change of phosphate to phosphorothioate?
3. How sites of DNA thiolation are chosen?
4. The function and advantages of this phosphorothioate modification?