Nucleoside base modifications can alter the structures and dynamics of RNA molecules and are important in tRNAs for maintaining translational fidelity and efficiency. The unmodified anticodon stem-loop from Escherichia coli tRNA(Phe) forms a trinucleotide loop in solution, but Mg2+ and dimethylallyl modification of A37 N6 destabilize the loop-proximal base pairs and increase the mobility of the...