Last modified on 28 May 2001.

Figure 2. Stereo views of A:G and A:A base-pairs at helix ends in different strutural motifs from X-ray crystallography. NMR structures are omitted for clarity. The A in each base-pair is superimposed on the left of each panel. Chemical drawings were created using ISIS/Draw and stereo images were created using INSIGHT II.

1. Chemical drawing of the G:A sheared base-pair (G:A N3-amino, amino-N7 base-pair; Burkard et al., 1999b).
2. Front view of sheared A:G base-pairs: blue, GNRA tetraloop; yellow, E loop; green, tandem GA; red, helix end.
3. Side view of (b).
4. Chemical drawing of the G:A imino base-pair (G:A carbonyl-amino, imino-N1 base-pair; Burkard et al., 1999b).
5. Front view of imino A:G base-pairs: blue, 5' helix end; yellow, 3' helix end.
6. Side view of (e).
7. Chemical drawings of the A:A sheared-like base-pair (top; A:A N3-amino base-pair; Nagaswamy et al., 2000)) and the A:A imino-like base-pair (bottom; A:A N1-amino base-pair; Nagaswamy et al., 2000)).
8. Front view of A:A base-pairs: yellow, N1-amino conformation; blue, N3-amino conformation; red, N7-amino conformation; green, tandem; gray, triple.
9. Side view of (h).