The tRNA(Gly)/glycyl-tRNA synthetase (GlyRS) system belongs to the so-called 'class II aminoacyl-tRNA synthetase system' in which tRNA identity elements are assured by rather few and simple determinants mostly located in the tRNA acceptor stem. Regarding evolutionary aspects, the tRNA(Gly)/GlyRS system is a special case. There exist two different types of GlyRS, namely an archaebacterial/human type and a eubacterial type reflecting an evolutionary divergence within this system. Here we report the crystal structure of a human tRNA(Gly) acceptor stem microhelix at 1.2 angstrom resolution. The local geometric parameters of the microhelix and the water network surrounding the RNA are presented. The structure complements the previously published Escherichia coli tRNA(Gly) aminoacyl stem structure. (C) 2008 Elsevier Inc. All rights reserved.