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Figure 7.
Figure 7 Model of SelB bound to the GTPase activating centre of
the 70S ribosome prior to the release of the tRNA. (A)
Superposition of SelB domains I–III with the corresponding
domains from the EF-Tu:GDP:Phe-tRNA^Phe:kirromycin complex bound
to the 70S ribosome. After superposition of SelB (green) with
EF-Tu (red), SelB domain IV points towards the mRNA entrance
cleft of the small ribosomal subunit. The A/T state Phe-tRNA^Phe
from the EF-Tu complex is depicted in blue. CP: central
protuberance; L11: L11 region of the large subunit. (B) In the
schematic representation, the crown view of the 50S subunit is
shown (grey). Domain IV of SelB (green), which points towards
the mRNA entrance cleft formed by the 30S subunit (yellow
outline), would allow SelB to bind the SECIS element located in
the 3' UTR of the mRNA (red) either directly or via an adapter
protein. Sec-tRNA^Sec (blue) bound to SelB:GTP would recognize
the internal UGA stop codon located in the A site of the small
ribosomal subunit (shown as 'stop signal'). The usual UAA or UAG
stop codon of the gene is indicated with a red dot, and the
tRNAs located in the P and E sites are depicted in magenta and
brown, respectively. L1: large ribosomal protein L1; CP: central
protuberance; L11: L11 region of the large subunit.
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