Alterations of binding mode and cutting site by G-->I replacement in preferred cleavage sequences 5'-AGG of chromoprotein C-1027.

Replacement of guanosine by inosine at the center position of a target trinucleotide 5'-AGG resulted in greatly diminished DNA cleavage by C-1027 chromophore, indicating that the guanine 2-amino group significantly participates to DNA binding and cleavage by the chromophore of C-1027. This notion was supported by fluorescence titrations of the chromophore with [poly(dG-dC)]2 and [poly(dI-dC)]2. In preferred cleavage sequence 5'-AGG of the enediyne chromophore of C-1027, the G-->I substitution clearly induces change of DNA binding mode and cutting site.