FIGURE 4.

Positions of universal bases in the secondary structure of 16S rRNA. Universally conserved (C = 2.000) bases are indicated in boldface on a diagram of the secondary structure of the E. coli 16S rRNA (Cannone et al. 2002; this work). Nucleotides are numbered at every ten positions; large numbers indicate the numbering for the 45 different helical elements. Several prominent universal clusters can be seen, many of which correspond to functional sites of the small ribosomal subunit (Fig. 6).