1.   This phenomena is consistent with the formation of intrastrand crosslinks between adjacent guanine residues on the template strand.

2.   The arrows indicate the positions of the guanine residues in each half of the dimer.

3.   We propose a model in which bleomycin cleavage is determined by local DNA structure, while strong binding requires the presence of a guanine residue.

4.   The central guanine residues are indicated by the arrows.