This family is found at the N-terminus of the pre-pilin peptidases (pfam01478). It's function has not been specifically determined; however some of the family have been characterized as bifunctional, and this domain may contain the N-methylation activity (EC:2.1.1.-). It consists of an intracellular region between a pair of transmembrane. This region contains an invariant proline and two almost fully conserved disulphide bridges - hence the name DiS-P-DiS. The cysteines have been shown to be essential to the overall function of the enzyme in, but their role was incorrectly ascribed.