Methylnitronitrosoguanidine

Methylnitronitrosoguanidine (MNNG or MNG) is a biochemical tool used experimentally as a carcinogen and mutagen. It acts by adding alkyl groups to the O of guanine and O of thymine, which can lead to transition mutations between GC and AT. These changes do not cause a heavy distortion in the double helix of DNA and thus are hard to detect by the DNA mismatch repair system.