Abstract
A Research Article in this issue of Science by P. Nissen et al . ( p. 1464 ) reports the crystal structure of elongation factor Tu (EF-Tu) complexed with tRNA and GTP. In his Perspective, P. Moore discusses the similarity between this new structure and the GDP-bound form of elongation factor G. Three domains at the carboxyl-terminal end of EF-G, which have no homologs in EF-Tu, together resemble tRNA and are positioned like the tRNA bound to EF-Tu.