type III site-specific deoxyribonuclease complex
type iii site-specific deoxyribonuclease complex
"A heterodimeric enzyme complex composed of two subunits, Res and Mod, that functions as an endonuclease and cleaves DNA. Cleavage will only occur when there are two un-methylated copies of a specific recognition site in an inverse orientation on the DNA. Cleavage occurs at a specific distance away from one of the recognition sites. The Mod subunit can act alone as a methyltansferase. DNA restriction systems such as this are used by bacteria to defend against phage and other foreign DNA that may enter a cell."