Crystal structures of an unmodified bacterial tRNA reveal intrinsic structural flexibility and plasticity as general properties of unbound tRNAs

Residues comprising the E. coli tRNA^Asp TΨC loop exhibit a T-loop structural fold in a context-independent manner. (A) TΨC loop in the crystal structure of full-length E. coli tRNA^Asp assumes the canonical T-loop conformation while engaging in tertiary interactions with D loop residues (yellow) acting as intercalating and stacked nucleobases. (B) TΨC loop in the crystal structure of E. coli tRNA^Asp-AS/TSL reveals a T-loop conformation, despite the absence of the D loop interactions, and not a UUCG tetraloop conformation (illustrated in C), as could be expected from sequence analysis.