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How the ribosome hands the A-site tRNA to the P site during EF-G–catalyzed translocation

Science  05 Sep 2014:
Vol. 345, Issue 6201, pp. 1188-1191
DOI: 10.1126/science.1255030

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Caught in the act of making protein

The ribosome is a large RNA-protein complex that converts the genetic code stored in messenger RNA (mRNA) into proteins. Zhou et al. have determined the structure of a bacterial ribosome caught in the act of decoding an mRNA. Transfer RNAs (tRNAs) decipher the genetic code in the mRNA to ensure that the ribosome uses the correct amino acids. The structure shows tRNAs in the process of being moved between successive protein-building binding pockets as the ribosome reads the mRNA like a piece of old-fashion computer tape.

Science, this issue p. 1188

Abstract

Coupled translocation of messenger RNA and transfer RNA (tRNA) through the ribosome, a process catalyzed by elongation factor EF-G, is a crucial step in protein synthesis. The crystal structure of a bacterial translocation complex describes the binding states of two tRNAs trapped in mid-translocation. The deacylated P-site tRNA has moved into a partly translocated pe/E chimeric hybrid state. The anticodon stem-loop of the A-site tRNA is captured in transition toward the 30S P site, while its 3′ acceptor end contacts both the A and P loops of the 50S subunit, forming an ap/ap chimeric hybrid state. The structure shows how features of ribosomal RNA rearrange to hand off the A-site tRNA to the P site, revealing an active role for ribosomal RNA in the translocation process.

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