Two bases are eliminated from DNA by treatment with bleomycin or with hemin-intercalators

A hemin-intercalator, H4G-His, which possesses 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) as an intercalator moiety and histidine as an intramolecular ligand of the ferrous ion of the hemin ring, cleaves DNA very efficiently, and acts at guanine-pyrimidine sequences preferentially. Bleomycin (BLM) also cleaves DNA with the same base-sequence selectivity shown by H4G-His. The 5'-terminal of the DNA fragments cleaved by H4G-His or by BLM bears a phosphoryl group, while the 3'-terminal of the cleaved DNA fragments does not possess a 3'-phosphoryl group. There are three (or more) kinds of structures of the 3'-terminals. One of the structures of the 3'-terminals of the cleaved DNA fragments is a free 3'-hydroxy group. We propose that there exist plural mechanisms for DNA cleavage by H4G-His or by BLM, one of which involves elimination of two bases from DNA.