SOLUTION STRUCTURE OF THE TERNARY COMPLEX BETWEEN AMINOACYL-TRANSFER-RNA, ELONGATION-FACTOR TU, AND GUANOSINE TRIPHOSPHATE

Complex formation between elongation factor Tu (EF-Tu), Phe-tRNA(Phe), and GTP was analyzed by small-angle neutron and X-ray scattering meth ods. Both techniques show that the ternary complex consists of one EF- Tu and one aminoacyl-tRNA. No shift in stoichiometry was detected when the temperature was raised from 5 to 37 degrees C, in contrast to pre vious observations obtained from RNase A protection experiments [Bilgi n and Ehrenberg (1995) Biochemistry 34, 715-719]. A small but signific ant increase in the radius of gyration of the complex was observed whe n the temperature was decreased from 37 to 5 degrees C. The X-ray solu tion scattering patterns were compared with those calculated from the crystal structure of the complex formed between EF-Tu from Thermus aqu aticus and Phe-tRNA(Phe) from yeast. The comparison shows that the sol ution structure of the ternary complex, formed entirely from Escherich ia coli components and under translationally optimal buffer conditions ? is very close to the crystal structure, formed from heterologous com ponents under very different conditions. Furthermore, for the hybrid c omplex in solution there is no evidence for the formation of trimers a s suggested by the crystal structure.