FIGURE 6.

Universal clusters. Clusters of invariant nucleotides are indicated by their numbers. Many of the clusters can be assigned to ribosomal functions, as presented in Table 3. These include the binding sites for A-site (clusters 2, 3, 5, 6, and 7) and P-site (clusters 4, 8, and 9) tRNAs (Moazed and Noller 1990; Ogle et al. 2001; Yusupov et al. 2001; Selmer et al. 2006), sites of interaction with elongation factor EF-G (clusters 5, 6, 7, 14, and 15) (Gao et al. 2009; Brilot et al. 2013; Zhou et al. 2013) and sites of contact with the 50S subunit at intersubunit bridges B2c and B3 (clusters 12 and 13) (Yusupov et al. 2001; Selmer et al. 2006).