Wang, LR; Chen, S; Xu, TG; Taghizadeh, K; Wishnok, JS; Zhou, XF; You, DL; Deng, ZX; Dedon, PC  (2007).  Phosphorothioation of DNA in bacteria by dnd genes.  NATURE CHEMICAL BIOLOGY,  3:709-710.  [Full Text] 
(Featured by Fritz Eckstein in Nat Chem Biol. 2007 3(11):689-690 [Full Text ] and Reported by Chemical & Engineering News Oct. 22, 2007, 14)
Modifications of the canonical structures of DNA and RNA play critical roles in cell physiology, DNA replication, transcription and translation in all organisms. We now report that bacterial dnd gene clusters incorporate sulfur into the DNA backbone as a sequence-selective, stereospecific phosphorothioate modification. To our knowledge, unlike any other DNA or RNA modification systems, DNA phosphorothioation by dnd gene clusters is the first physiological modification described on the DNA backbone.