Abstract
A ribooligonucleotide microhelix derived from the acceptor stem of Escherichia coli tRNA Ala having a C3-A70 mismatch in place of the G3-U70 wobble pair in the wild-type tRNA Ala, and a sequence variant with a regular U3-A70 base pair have been investigated by NMR. In vivo, suppressor tRNA Ala variants with C3-A70 (as well as several other) mismatch pairs are substrates for alanyl-tRNA synthetase (ARS), supporting the hypothesis of an `indirect' recognition of the identity element 3-70 mismatch pair via structural modifications caused by the mispair in comparison to canonical A-RNA helices. It is demonstrated that the C-A mismatch likewise induces helix geometry alterations, in particular with respect to base stacking in the vicinity of the mismatch. However, with reference to the `wild-type' G3-U70 microhelix, destacking in the C3-A70 acceptor stem duplex occurs in the opposite direction from the mismatch pair. Therefore it is concluded that the locally enhanced conformational flexibility or dynamics associated with the structural changes induced by the mismatch pairs could be an essential prerequisite for optimal adaptation of the tRNA Ala acceptor stem to the contact region of the ARS.
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