FIGURE 3.

Secondary structure of the human 18S rRNA showing differences in DMS reactivity of nucleotides in 80S ribosomes compared with 40S subunits. Shaded regions where changes in chemical reactivity occur are enlarged below and to the right of the secondary structure. Squares show enhancements in reactivity; arrows, reduced reactivity. The secondary structure map is from Cannone et al. (2002). The domain organization of 18S rRNA is indicated on the secondary structure, as are helices in E. coli numbering relevant to the main text. The sequence register for human 18S rRNA is indicated by gray numbers for nucleotides divisible by 50, and gray dashes underlining nucleotides divisible by 10.