dndDB: a database focused on phosphorothioation of the DNA backbone.

The Dnd DNA degradation phenotype was first observed during electrophoresis of genomic DNA from Streptomyces lividans more than 20 years ago. It was subsequently shown to be governed by the five-gene dnd cluster. Similar gene clusters have now been found to be widespread among many other distantly related bacteria. Recently the dnd cluster was shown to mediate the incorporation of sulphur into the DNA backbone via a sequence-selective, stereo-specific phosphorothioate modification in Escherichia coli B7A. Intriguingly, to date all identified dnd clusters lie within mobile genetic elements, the vast majority in laterally transferred genomic islands.