The 1.2A crystal structure of an E. coli tRNASer)acceptor stem microhelix reveals two magnesium binding sites.

Abstract tRNA identity elements assure the correct aminoacylation of tRNAs by the cognate aminoacyl-tRNA synthetases. tRNA Ser belongs to the so-called class II system, in which the identity elements are rather simple and are mostly located in the acceptor stem region, in contrast to ‘class I’, where tRNA determinants are more complex and are located within different regions of the tRNA. The structure of an Escherichia coli tRNA Ser acceptor stem microhelix was solved by high resolution X-ray structure analysis. The RNA crystallizes in the space group C 2, with one molecule per asymmetric unit and with the cell constants a  = 35.79, b  = 39.13, c  = 31.37 A, and β  = 111.1°. A defined hydration pattern of 97 water molecules surrounds the tRNA Ser acceptor stem microhelix. Additionally, two magnesium binding sites were detected in the tRNA Ser aminoacyl stem.