FIGURE 3.

The interaction between nucleotides −2P and −2Q (A–E) and between −2R and −2S (F–H) in different cases of the A-wedge motif (see text). (Black) Nucleotides −2Q and −2S; (gray) other nucleotides; (dashed lines) hydrogen bonds. The numbers of nucleotides in rRNA are indicated, when necessary. The angle between bases −2R and −2S (F–H) is sharper than between bases −2P and −2Q (A–E). Correspondingly, the interbase H-bonds between −2R and −2S are less favorable than between −2P and −2Q.