The time and temperature dependence of the intrinsic fluorescence of double-stranded d(CTGA[2AP]TTCAG)2 DNA decamer containing a modified adenine base, 2AP, show that the bases exists in at least four distinct, interconverting conformations. The melting transition of the duplex governs the equilibrium of these states. Measurements on a purely singlestranded decamer facilitate the interpretation of data. States are identified as completely unstacked, maximally stacked, and partially stacked, according to state fluorescence lifetimes and the temperature dependence of lifetimes and populations. The equilibrium of state populations in the single-stranded decamer is described accurately by simple enthalpy and entropy differences, where linear ln [population] vs. 1/T plots are observed. Similar plots for the double-stranded show nonlinearities. The cooperative melting transition of the double-stranded decamer is reflected most strongly in the interconversion of the completely unstacked state with a partially-stacked state. This completely unstacked state is not the "unstacked" state assumed in UV absorption hypochromicity measurements.

Date Published: 1 May 1990
PDF: 8 pages
Proc. SPIE 1204, Time-Resolved Laser Spectroscopy in Biochemistry II, (1 May 1990); doi: 10.1117/12.17767

Published in SPIE Proceedings Vol. 1204:
Time-Resolved Laser Spectroscopy in Biochemistry II
Joseph R. Lakowicz, Editor(s)