Table 2. Qualitative TTA/UUA loop descriptors in terms of base stacking.
| Loop type | Stacked bases | Mutually perpendicular bases | Orientation of 3rd base |
|---|---|---|---|
| 1 | T1, A3 | T2, A3 | T2 close to A3 |
| 2 | T1, T2 | - | A3 away from T1, T2 |
| 3 | T2, A3 | T1, A3 | T1 close to A3 |
| 4 | - | T2, A3 | T1 away from T2, A3 |
| 5 | T2, A3 | - | T1 close to T2, A3 |
| 6 | T2, A3 | T1 | T1 away from T2, A3 |
| 7 | T2, A3 | T1 close to T2 | |
| 8 | U2, A3 | U1 | U1 away from U2, A3 |
| 9 | No stacking | - | All away from each other |
| 10 | T2, A3 | - | T1 away from T2, A3 |
| 11 | No stacking | T1, T2 | A3 close to T1 |
| 12 | T2, A3 | - | T1 away from T2, A3 |