Internal loop free energies: initiation 4 1.1 5 2.0 6 2.0 Asymmetry 0.6 AU/GU closure: 0.7 2x3 terminal mismatch: YR/AG -0.5 RY/GA -1.2 YR/GA -1.1 GG -0.8 UU -0.4 Other terminal mismatch: AG -0.8 GA -1.0 GG -1.2 UU -0.7