FLUORESCENCE PROPERTIES OF A NEW GUANOSINE ANALOG INCORPORATED INTO SMALL OLIGONUCLEOTIDES

The fluorescence properties of 3-methyl-isoxanthopterin (3-MI) incorpo rated into different oligonucleotides have been determined. This highl y fluorescent guanosine analog has its absorption and fluorescence spe ctra well resolved from those of the normal nucleotides and the aromat ic amino acids. The small shifts observed in absorption and fluorescen ce emission spectra upon incorporation of 3-MI into these oligonucleot ides are consistent with a general solvent effect and do not suggest a ny contribution from the position of the probe from the 5' end, the se quence of nucleotides immediately 5' or 3' to the probe, or the single -or double-stranded nature of the oligomer. However, steady-state and time-resolved fluorescence studies indicate that the presence of a pur ine immediately 5' or 3' to the probe results in some dynamic but most ly static quenching in the single-stranded oligomer. Furthermore, a 3' purine is more effective than a 5' purine, and an adenine appears to be more effective than a guanine for these static quenching interactio ns. Formation of the double-stranded oligomer leads to an additional l oss of quantum yield, which can also be ascribed primarily to static q uenching. These results show that this new class of spectrally enhance d fluorescent purine analogs will be able to provide useful informatio n concerning the perturbation of nucleic acid structures.