tmRNA secondary structure model with indicated nucleotide positions displaying changed susceptibility to lead(II) acetate. Specifically exposed or protected nucleotides identified in experiments in Figures 1 and 5 were mapped on the secondary structure of tmRNA Adapted with permission from Fig. 1A in Zwieb et al. (1999) (© Oxford University Press). Empty blue squares mark the exposed nucleotides and filled red circles mark the protected nucleotides. The tRNA-like domain (TLD) and the mRNA-like domain (MLD) are indicated on the structure as well as pseudoknots 1–4 (PK1–PK4) and helices 2 and 4 (h2, h4). The lead(II) cleavages occur in the backbone of tmRNA on the 3′ side of marked nucleotides (e.g., cleavage at U10 occurs between U10 and C11).
