During protein synthesis, the ribosome selects aminoacyl-tRNAs with anticodons matching the mRNA codon present in the A-site of the small ribosomal subunit. The aminoglycoside antibiotic streptomycin disrupts decoding by binding close to the site of codon recognition. Here we use X-ray crystallography to define the impact of streptomycin on the decoding site of the Thermus thermophilus 30S ribosomal subunit in complexes with cognate or near-cognate anticodon stem-loop analogs (ASLs) and mRNA. Our crystal structures display a significant local distortion of 16S rRNA induced by streptomycin, including the crucial bases A1492 and A1493 that participate directly in codon recognition. Consistent with kinetic data, we observe that streptomycin stabilizes the near-cognate ASL complex, while destabilizing the cognate ASL complex. These data reveal how streptomycin disrupts the recognition of cognate ASLs and yet improves recognition of a near-cognate ASL.

Polyphenol Oxidase from Apple (Malus domestica Borkh. cv Bramley's Seedling): Purification Strategies and Characterization was 30 °C and the enzyme had residual activity of greater than 50% during storage for 72 h at 20 °C to 30 °C and was 30 °C and the enzyme had residual activity of greater than 50% during storage for 72 h at 20 °C to 30 °C and was 30 °C and the enzyme had residual activity of greater than 50% during storage for 72 h at 20 °C to 30 °C and was 30 °C and the enzyme had residual activity of greater than 50% during storage for 72 h at 20 °C to 30 °C and for 24 h at 40 °C to 50 °C.Of the substrates tested, activity was greatest with 4-methylcatechol followed by for 24 h at 40 °C to 50 °C. Of the substrates tested, activity was greatest with 4-methylcatechol followed by for 24 h at 40 °C to 50 °C. Of the substrates tested, activity was greatest with 4-methylcatechol followed by for 24 h at 40 °C to 50 °C. Of the substrates tested, activity was greatest with 4-methylcatechol followed by for 24 h at 40 °C to 50 °C. Of the substrates tested, activity was greatest with 4-methylcatechol followed by catechol, pyrogallol, and (-)-epicatechin. The most effective inhibitors tested were sodium metabisulfite and catechol, pyrogallol, and (-)-epicatechin. The most effective inhibitors tested were sodium metabisulfite and catechol, pyrogallol, and (-)-epicatechin. The most effective inhibitors tested were sodium metabisulfite and catechol, pyrogallol, and (-)-epicatechin. The most effective inhibitors tested were sodium metabisulfite and catechol, pyrogallol, and (-)-epicatechin. The most effective inhibitors tested were sodium metabisulfite and ascorbic acid. ascorbic acid. ascorbic acid. ascorbic acid. ascorbic acid.

The ribosome decodes mRNA by monitoring the geometry of codon-anticodon base-pairing using a set of universally conserved 16S rRNA nucleotides within the conformationally dynamic decoding site. By applying single-molecule FRET and X-ray crystallography, we have determined that conditional-lethal, streptomycin-dependence mutations in ribosomal protein S12 interfere with tRNA selection by allowing conformational distortions of the decoding site that impair GTPase activation of EFTu during the tRNA selection process. Distortions in the decoding site are reversed by streptomycin or by a second-site suppressor mutation in 16S rRNA. These observations encourage a refinement of the current model for decoding, wherein ribosomal protein S12 and the decoding site collaborate to optimize codon recognition and substrate discrimination during the early stages of the tRNA selection process.