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 be transformed into B form upon interaction with 4',6-diamidino-2-phenylindole (DAPI). The Z --> B transformation is complete at a mixing ratio 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 between DAPI and poly [d(G-m5C)2] in its Z form at low drug: DNA ratios is suggested from optical dichroism and time-resolved luminescence anisotropy results. The spectroscopic behaviour of DAPI indicates that the Z conformation of DNA does not provide normal binding sites for DAPI, such as groove or intercalation sites, but that the initial association may be of external nature. (C) 1993 John Wiley & Sons, Inc.