Thermodynamic parameters for an expanded nearest-neighbor model for formation of RNA duplexes with Watson-Crick base pairs
T. Xia, J. S. Jr., M. E. Burkard, R. Kierzek, S. J. Schroeder, X. Jiao, C. Cox, and D. H. Turner
Biochemistry, vol. 37, pp. 14 719–14 735, 1998.
Improved thermodynamic parameters for prediction of RNA duplex formation are derived
from optical melting studies of 90 oligoribonucleotide duplexes containing only Watson-Crick base pairs.
To test end or base composition effects, new sets of duplexes are included that have identical nearest
neighbors, but different base compositions and therefore different ends. Duplexes with terminal GC pairs
are more stable than duplexes with the same nearest neighbors but terminal AU pairs. Penalizing terminal
AU base pairs by 0.45 kcal/mol relative to terminal GC base pairs significantly improves predictions of
$\Delta G°37 $ from a nearest-neighbor model. A physical model is suggested in which the differential treatment
of AU and GC ends accounts for the dependence of the total number of Watson-Crick hydrogen bonds
on the base composition of a duplex. On average, the new parameters predict $\Delta G°37 $, $\Delta H° $, $\Delta S° $, and $T_M$
within 3.2%, 6.0%, 6.8%, and 1.3 °C, respectively. These predictions are within the limit of the model,
based on experimental results for duplexes predicted to have identical thermodynamic parameters.