RIBOSOME BINDING OF DNA ANALOGS OF TRANSFER-RNA REQUIRES BASE MODIFICATIONS AND SUPPORTS THE EXTENDED ANTICODON

The efficiency of translation depends on correct tRNA-ribosome interactions. The ability of chemically synthesized yeast tRNA(Phe) anticodon domains to effectively inhibit the binding of native yeast tRNA(Phe) to poly(U)-programmed Escherichia coli 30S ribosomal subunits was dependent on a Mg2+-stabilized stem and an open anticodon loop, both facilitated by base modifications. Analysis of tRNA sequences has revealed that base modifications which negate canonical hydrogen bonding are found in 95% of those tRNA anticodon loop sequences with the potential to form two Watson-Crick base pairs across the loop. Therefore, we postulated that astable anticodon stem and an open loop are prerequisites for ribosome binding. To test this hypothesis, DNA analogs of the yeast tRNA(Phe) anticodon domain were designed to have modification-induced, Mg2+-stabilized stems and open loops. The unmodified DNA analog neither bound to poly(U)-programmed 30S ribosomal subunits nor inhibited the binding of native tRNA(Phe) However, specifically modified DNA analogs did bind to ribosomal subunits and effectively inhibited tRNA(Phe) from binding. Thus, modification dependent, Mg2+-stabilized anticodon domain structures with open loops have evolved as the preferred anticodon conformations for ribosome binding.