D arm

The D arm is a feature in the tertiary structure of transfer RNA (tRNA). It is composed of the two D stems and the D loop. The D loop contains the base dihydrouridine (D), for which the arm is named.^[1] The D loop's main function is that of recognition. It is widely believed that it acts as a recognition site for aminoacyl-tRNA synthetase, an enzyme involved in the aminoacylation of the tRNA molecule.^[1][2] The D stem is also believed to have a recognition role although this has yet to be verified.

Transfer RNA

It is a highly variable region and is notable for its unusual conformation due to the over-crowding on one of the guanosine residues. It appears to play a large role in the stabilization of the tRNA's tertiary structure. The role of the D nucleotide in tRNA structure has been demonstrated in a detailed study comparing the structure of the D arm of the Schizosaccharomyces pombe tRNA_i^Met with an unmodified uracil (U) to the structure with the modified D nucleotide.^[3] Despite the importance of the D am in many tRNAs, the D arm is absent from some mitochondrial tRNAs from metazoa.^[4]