All 64 possible thermodynamic parameters
for a single-bulge loop in the middle o
f a sequencewere derived
from optical melting studies. The relative stability o
f a single bulge depended on both thetype o
f bulged base and its
flanking base pairs. The contribution o
f the single bulge to helix stabilityranged
from 3.69 kcal/mol
for a T
AT bulge to -1.05 kcal/mol
for an A
CC bulge. Thermodynamics
for10 sequences with a G
TG bulge were determined to test the applicability o
f the nearest-neighbor modelto a single-bulge loop. Thermodynamic parameters
for the G
TG bulge and Watson-Crick base pairspredict
f">,
fchars/Delta.gi
f" BORDER=0 >
Hf">,
fchars/Delta.gi
f" BORDER=0 >
Sf">, and
TM(50
f">M) values with average deviations o
f 3.0%, 4.3%, 4.7%, and 0.9
f">C, respectively. The prediction accuracy was within the limits o
f what can be expected
for a nearest-neighbor model. This certi
fied that the thermodynamics
for single-bulge loops can be estimated adequatelyusing a nearest-neighbor model.