"Hot spots" associated with the photoinduced binding of cis-dichloro bis(1,10 phenanthroline)rhodium(III) chloride to HIV-1 and c-raf DNA

The octahedral rhodium complex, cis-dichloro bis(1,10 phenanthroline)rhodiu m(III) chloride (BISPHEN), is known to form covalent linkages with DNA invo lving the attachment of the metal to a base, In order to determine the sequ ence selectivity of this chemistry, solutions of the complex containing one of the double-stranded DNA plasmids, pBSSK.c-raf (eco) or pBSKS(+).XE.LTR- F (a construct that contains sequences derived from the long terminal repea t [LTR] region of the human immunodeficiency virus) have been irradiated us ing UVA light. The DNA samples were denatured after irradiation, a primer w as annealed to one of the strands, and a complementary strand was construct ed using a polymerase enzyme. Polyacrylamide gel sequencing analysis was us ed to reveal stops created in the complementary strand caused by the polyme rase encountering a metal-bound base. The data indicate that "hot spots" pr imarily occur at, or adjacent to, guanines (G), with a particularly strong preference for strings of G, In the latter case, the hottest spot is at the 5'G, These results are consistent with our previously postulated mechanism for the covalent binding chemistry which involves photooxidation of deoxyg uanosine by the elicited state of the metal complex as the primary photoche mical step.