This model describes the DndB protein encoded by an operon associated with a sulfur-containing modification to DNA. The operon is sporadically distributed in bacteria, much like some restriction enzyme operons. DndD is described as a putative ATPase. The small number of examples known so far include species from among the Firmicutes, Actinomycetes, Proteobacteria, and Cyanobacteria. [DNA metabolism, Restriction/modification]