Structure of a photoactive rhodium complex intercalated into DNA

Intercalating complexes of rhodiun(III) are strong photo-oxidants that prom ote DNA strand cleavage or electron transfer through the double helix The 1 .2 Angstrom resolution crystal structure of a sequence-specific rhodium int ercalator bound to a DNA helix provides a rationale for the sequence specif icity of rhodium intercalators. It also explains how intercalation in the c enter of an oligonucleotide modifies DNA conformation. The rhodium complex intercalates via the major groove where specific contacts are formed with t he edges of the bases at the target site. The phi ligand is deeply inserted into the DNA base pair stack The primary conformational change of the DNA is a doubling of the rise per residue, with no change in sugar pucker from B-form DNA. Based upon the five crystallographically independent views of a n intercalated DNA helix observed in this structure, the intercalator may b e considered as an additional base pair with specific functional groups pos itioned in the major groove.