Z-]B TRANSITION IN POLY[D(G-M5C)2] INDUCED BY INTERACTION WITH 4',6-DIAMIDINO-2-PHENYLINDOLE

The Z form of poly [d(G-m5C)2], in presence of Mg2+ ion, is found to b e transformed into B form upon interaction with 4',6-diamidino-2-pheny lindole (DAPI). The Z --> B transformation is complete at a mixing rat io of about 0.07 DAPI per DNA base pairs, i.e., each DAPI molecule may be related to the conversion of 6-7 base pairs. An interaction betwee n DAPI and poly [d(G-m5C)2] in its Z form at low drug: DNA ratios is s uggested from optical dichroism and time-resolved luminescence anisotr opy results. The spectroscopic behaviour of DAPI indicates that the Z conformation of DNA does not provide normal binding sites for DAPI, su ch as groove or intercalation sites, but that the initial association may be of external nature. (C) 1993 John Wiley & Sons, Inc.