HEXAMMINECOBALT(III) CHLORIDE ASSISTED, VISIBLE-LIGHT INDUCED, SEQUENCE-DEPENDENT CLEAVAGE OF DNA

9-Anthracene methyl ammonium chloride (AMAC) cleaves supercoiled pUC18 DNA with a marked preference for 3'-AG-5' sites when the reaction mix ture is irradiated with blue light (390 nm) in the presence of hexammi necobalt(III) chloride (CoHA). Irradiation of pUC18 DNA in the presenc e of either CoHA or AMAC alone, led to poor photocleavage, establishin g a strong synergistic effect for the DNA nicking reaction. Irradiatio n of a mixture of AMAC and CoHA in the absence of DNA led to the photo oxidation of AMAC to anthraquinone. Time resolved fluorescence studies show that AMAC fluorescence is quenched by DNA in a base sensitive ma nner. AMAC emission is quenched by CoHA at diffusion controlled rate, and the quenching events may involve electron transfer from AMAC to Co HA. The DNA may facilitate bimolecular electron transfer between the D NA-bound AMAC, and CoHA. The cation radical resulting from AMAC oxidat ion by CoHA is suggested to result in DNA cleavage. DNA sequencing exp eriments reveal preferential cleavage at 3'-AG-5' sites. Among these c leavage sites, 3'-AGG-5' sequences were associated with higher intensi ties. Only one out of 9 observed cleavage sites is not a 3'-AGG-5' seq uence, instead it was a 3'-TGC-5' site, containing a central G flanked by T/C instead of A/G. Little or no cleavage is observed at 3'-GCA-5' , or 3'-TGT-5' sites. Several visible light absorbing agents bind to D NA at specific sites, and current observations may open the possibilit y of using these binding agents for sequence dependent photo-cleavage of DNA. (C) 1997 Elsevier Science Inc.