Figure 1. 5¢ and 3¢ ends of 16S rRNA within the 30S subunit (a) and of 23S rRNA within the 50S subunit (b) viewed from the interface. (a) 30S subunit; Thermus thermophilus 30S (pdb 1fka): Ribbon representation of rRNA with the 5¢ and 3¢ ends of the 16S rRNA coloured green and red, respectively. The residues U6 (green) and C1512 (red) are in spacefill and are approximately 80 Å apart. (b) 50S subunit; Deinococcus radiodurans 50S (1kpj): Ribbon representation of rRNA with the 5¢and 3¢ ends of the 23S rRNA coloured green and red, respectively. The residues G1 (green) and A2877 (red) are shown in spacefill and are in contact with one another.

Figure 2. Translational regulation of the r-proteins. Usually the second or third cistron of a polycistronic mRNA codes for an rRNA-binding protein which can also bind to the region of the ribosomal-binding site of the first cistron of its own mRNA, thus competing with initiating 30S subunits. Therefore, this regulatory protein will inhibit the translation of its own polycistronic mRNA when a significant free pool of this protein is in the cell. Nine regulatory r-proteins have been identified: S4, S7, S8, S15, S20, L1, L4, L10 and L20.

Figure 3. The core structure (red lines) common to all 16S-type rRNAs from ribosomes of various organisms. (a) E. coli; (b) Halobacterium volcanii; (c) yeast, cytoplasmic ribosomes; and (d) mitochondria of plants (maize). From Gutell RR, Weiser B, Woese CR and Noller HF (1985) Comparative anatomy of 16S-like ribosomal RNA. Progress in Nucleic Acid Research and Molecular Biology 32: 155–216.

Figure 4. Assembly maps of the ribosome from E. coli. (a) The small 30S subunit. Proteins boxed in are those either required for the formation of RI₃₀* particles or found in the isolated 21S particles. Modified from Held WA, Ballou B, Mizushima S and Nomura M (1974) Journal of Biological Chemistry 249: 3103–3111. (b) The large 50S subunit. The three main fragments of 23S rRNA (13S, 8S and 12S) are indicated, and proteins are arranged according to their binding regions on 23S rRNA. The proteins boxed in are required for the transition RI₅₀(1) RI₅₀(1)* of the early assembly. Proteins above the blue dotted line are those found in the RI₅₀(1) particles. L5, L15 and L18, in the triangle, are the proteins important for mediating the binding of 5S rRNA to 23S rRNA. Modified from Herold M and Nierhaus KH (1987) Journal of Biological Chemistry 262: 8826–8833.

Figure 5. Ribosomal secondary and tertiary structures within the ribosome; the domains are marked with the same colour in the secondary (a, c) and the tertiary structures (b, d). (a) Secondary structure of T. thermophilus 16S rRNA, with its 5¢, central, 3¢-major and 3¢-minor domains shaded in blue, magenta, red and yellow, respectively. (b) Three-dimensional fold of 16S rRNA in 70S ribosomes, with its domains coloured as in (a). (c) Secondary structures of T. thermophilus 23S and 5S rRNAs, indicating domains I (blue), II (cyan), III (green), IV (yellow), V (red) and VI (magenta) of 23S rRNA. The rRNAs are numbered according to E. coli. (d) Three-dimensional folds of 23S and 5S rRNAs, with their domains coloured as in (c). Modified from Yusupov MM et al. (2001) Science 292: 883–896.