tRNA identity elements determine the correct aminoacylation by the cognate aminoacyl-tRNA synthetase. In class It aminoacyl tRNA synthetase systems, tRNA specificity is assured by rather few and simple recognition elements, mostly located in the acceptor stem of the tRNA. Here we present the crystal structure of an Escherichia coli tRNA(Gly) aminoacyl stem microhelix at 2.0 angstrom resolution. The tRNA(Gly) microhelix crystallizes in the space group P3(2)21 with the cell constants a = b = 35.35 angstrom, c = 130.82 angstrom, gamma = 120 degrees. The helical parameters, solvent molecules and a potential magnesium binding site are discussed. (C) 2007 Elsevier Inc. All rights reserved.