Table 2. Torsional Parameters and/or 3J for A-Form RNA and Measured for Tetramersa.
| torsion | A-form101,104,113 | r(AAAA) | r(CAAU) | r(GACC) | r(UUUU) |
|---|---|---|---|---|---|
| β2 | T | 3.8, 1.0; T | 3.7, 2.2, ∼96% T | 3.7, 0.9; ∼100% T | 2.0, 2.0; ∼100% T |
| β3 | T | 3.0, 1.0; T | 3.5, <1, ∼100% T | 4.0, 2.0; ∼100% T | 2.0, 2.0; ∼100% T |
| β4 | T | 3.2, 1.0; T | 3.8–4.3, 3.3, ∼92% T | 4.4, 2.0; ∼95% T | 2.0, 2.0; ∼100% T |
| γ1 | G+ | 3.8, 2.0; ∼77% G+ | 1.6, ∼3.75, ∼82% G+ | 4.6, 2.3; ∼66% G+ | 3.7, 2.8; ∼70% G+ |
| γ2 | G+ | ∼2, ∼1; ∼100% G+ | ∼2.8,∼2.1; ∼87% G+ | ∼2, ∼2; ∼96% G+ | ≈2.5, ≈2.5; ∼86% G+ |
| γ3 | G+ | 2.0, 2.0; ∼96% G+ | 2.0, 1.3; ∼93% G+ | 1.5, <1; ∼100% G+ | <≈2.5, ≈2.5; ∼86% G+ |
| γ4 | G+ | 2.0, 2.0; ∼96% G+ | 1.0, <1; ∼70% G+ | 1.8, 1.3; ∼100% G+ | overlap |
| ϵ1 | 185–280° | 8.0–8.9; 207–233° | 9.4–9.8; 218–230° | 9.3; 213–230° | 8.2; 210–218° |
| ϵ2 | 185–280° | 8.6–8.8; 210–225° | 8.4; 211–219° | 9.1; 213–229° | 7.8; 207–215° |
| ϵ3 | 185–280° | 8.3–8.4; 209–221° | 8.3; 210–219° | 9.0; 212–227° | 7.7; 207–215° |
| ν11 | 0.2–1.3 | 2.0 | ≈1 | 1.8 | 4.5 |
| ν21 | 3.3–6.0 | 3.4 | 4.5 | 4.4 | 4.7 |
| ν31 | 8.8–11.5 | 5.4–6.0 | 8.4 | 7.9 | 5.3 |
| ν12 | 0.2–1.3 | 1.0 | ≈1 | <1 | 5.2 |
| ν22 | 3.3–6.0 | 3.6 | 4.6 | 4.4 | 4.6 |
| ν32 | 8.8–11.5 | 7.3 | 8.3 | 8.9 | 5.5 |
| ν13 | 0.2–1.3 | 1.0 | 1.4 | <1 | 5.2 |
| ν23 | 3.3–6.0 | 4.0 | 4.3 | 4.0 | 4.8 |
| ν33 | 8.8–11.5 | 8.0 | 8.2–8.4 | 8.8 | 5.4 |
| ν14 | 0.2–1.3 | 2.75 | 3.7 | 2.5 | 3.7 |
| ν24 | 3.3–6.0 | overlap | 3.7 | 4.6 | overlap |
| ν34 | 8.8–11.5 | 6.0 | overlap | 7.2 | overlap |
a
NMR 3J scalar coupling values
imply A-form structure for r(AAAA), r(CAAU),
and r(GACC), where nucleotides are numbered 1 to 4 starting at the
5′ nucleotide (cf. Figure 3). All values
are in Hz unless specified. For ribose torsions, 3JH1′–H2′ = ν1, 3JH2′–H3′ = ν2, and 3JH3′–H4′ = ν3. 3J scalar coupling
values for the 3′ terminal nucleotides and for all r(UUUU)
nucleotides imply they have significant populations in the C2′–endo
state (eq 2). The % of β in the T conformation
can be estimated by eq 11a, and the % of
γ in the G+ conformation can be estimated with eq 11b.103 There is no
significance to the order of 3J with H5′/H5″
for deducing β and γ populations.
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