Recombinant Escherichia coli Ribosome-associated inhibitor A (raiA)

During stationary phase prevents 70S dimer formation, probably in order to regulate translation efficiency during transition between the exponential and the stationary phases. During environmental stress such as cold shock or excessive cell density at stationary phase, stabilizes the 70S ribosome against dissociation, inhibits translation elongation and increases translation accuracy. When normal growth conditions are restored, is quickly released from the ribosome. Has been suggested to inhibit translation elongation by blocking the A-site (aminoacyl-tRNA site). Has also been suggested to inhibit translation initiation by blocking the A-site and P-site (peptidyl-tRNA site) of the ribosome. At 15 degrees Celsius binds 30S subunits and stimulates their association with 50S subunits into idle 70S ribosomes. Crystallization with T.thermophilus 70S ribosomes shows it binds in the channel between the head and body of the 30S subunit, where mRNA, tRNAs, initiation factors IF1 and IF3 and elongation factor G would bind; this protein's extended tail follows the mRNA channel and probably prevents RMF binding, which would prevent ribosome dimerization. This protein also stabilizes the 30S head relative to the rest of the ribosome, which may also prevent dimerization. Counteracts miscoding (translation errors) particularly efficiently at magnesium concentrations close to those observed in vivo but less efficiently at higher concentrations. Counteraction of miscoding was shown to be stronger than inhibition of translation, suggesting that the former activity could be the main function of this protein in vivo.