Mutations in 23 S ribosomal RNA perturb transfer RNA selection and can lead to streptomycin dependence

Abstract

Escherichia coli ribosomes with a G to C transversion at position 2661 in 23 S ribosomal RNA are more accurate in tRNA selection than wild-type ribosomes. This enhanced accuracy is due to improved initial selection of ternary complexes rather than proofreading of aminoacyl tRNAs. The 2661C mutation reduces the binding rate of cognate ternary complexes to the A-site. This binding rate deficiency becomes dramatic when ribosomes also harbour an S12 mutation with a streptomycin-resistant, hyperaccurate phenotype. In this case, severe loss of kinetic efficiency in EF-Tu function leads to cell death. Streptomycin restores viability by increasing the association rate of ternary complex to these doubly altered ribosomes. The binding rate of EF-G to 2661C ribosomes is also reduced while the translocation rate is unaffected.