Due to the redundancy of the genetic code there exist six mRNA codons for arginine and several tRNAArg isoacceptors which translate these triplets to protein within the context of the mRNA. The tRNA identity elements assure the correct aminoacylation of the tRNA with the cognate amino acid by the aminoacyl-tRNA-synthetases. In tRNAArg, the identity elements consist or the anticodon, parts of the D-loop and the discriminator base. The minor groove of the acceptor stem interacts with the arginyl-tRNA-syntlletase. We crystallized different Escherichia coli tRNA(Arg) acceptor stem helices and solved the structure of the tRNAArg isoacceptor RR-1660 microhelix by X-ray structure analysis. The acceptor stem helix crystallizes in the space group P1 with the cell constants a = 26.28, b = 28.92, c = 29.00 angstrom, alpha = 105.74, beta = 99.01, gamma = 97.44 and two molecules per asymmetric unit. The RNA hydration pattern consists of 88 bound water molecules. Additionally, one glycerol molecule is bound within the interface of the two RNA molecules. (C) 2009 Published by Elsevier Inc.