Cleavage of phosphorothioated DNA and methylated DNA by the type IV restriction endonuclease ScoMcrA. LiuG. OuH. Y. WangT. LiL. TanH. ZhouX. RajakumarKumar DengZ. HeX. 2012 Many taxonomically diverse prokaryotes enzymatically modify their DNA by replacing a non-bridging oxygen with a sulfur atom at specific sequences. The biological implications of this DNA S-modification (phosphorothioation) were unknown. We observed that simultaneous expression of the dndA-E gene cluster from Streptomyces lividans 66, which is responsible for the DNA S-modification, and the putative Streptomyces coelicolor A(3)2 Type IV methyl-dependent restriction endonuclease ScoA3McrA (Sco4631) leads to cell death in the same host. A His-tagged derivative of ScoA3McrA cleaved S-modified DNA and also Dcm-methylated DNA in vitro near the respective modification sites. Double-strand cleavage occurred 16-28 nucleotides away from the phosphorothioate links. DNase I footprinting demonstrated binding of ScoA3McrA to the Dcm methylation site, but no clear binding could be detected at the S-modified site under cleavage conditions. This is the first report of in vitro endonuclease activity of a McrA homologue and also the first demonstration of an enzyme that specifically cleaves S-modified DNA.