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Role of Era in the maturation of 30S ribosomal subunit. The GTPase domain is represented by a grey rectangle, the KH domain by an orange oval, GTP and GDP by purple cartoons, and the conformations of ERA by numbers in red. The pre-30S particle and 30S r-subunit are represented by larger grey ovals. The pre-16S rRNA and 16S rNRA are represented by a grey line with embedded AUCACCUCC sequence. The unoccupied ERA-binding pocket in the pre-30S particle and that in the 30S r-subunit are indicated in white. The four functional states of ERA, including (A) apo-ERA, (B) ERA-GTP, (C) ERA-GTP-pre-30S, and (D) ERA-GDP, are represented by the apo-ERA (PDB: 1EGA), ERA-GNP (PDB: 1WF3), ERA-GNP-RNA (PDB: 3IEV), and ERA-GDP (PDB: 3IEU) structures. In panel C, the cleavage sites of RNase E, RNase G, and the unknown nuclease are indicated with numbered arrows 1, 2, and 3, respectively. (E) The pre-30S particle contains pre-16S rRNA. (F) The mature 30S r-subunit contains 16S rRNA. (G) The mature 30S r-subunit may bind apo-ERA in a distinct conformation 3 (PDB: 1X1L) (Chao Tu, Xiaomei Zhou et al. Proc. Natl. Acad. Sci. USA 106:14843-14848, 2009. PubMed: 19706445).