ROLES OF RESIDUES IN MAMMALIAN MITOCHONDRIAL ELONGATION-FACTOR TS IN THE INTERACTION WITH MITOCHONDRIAL AND BACTERIAL ELONGATION-FACTOR TU

The crystal structure of the complex between Escherichia coli elongati on factors Tu and Ts (EF-Tu.Ts) and subsequent mutagenesis work have p rovided insights into the roles of a number of residues in E. coli EF- Ts in its interaction with EF-Tu. The corresponding residues in bovine mitochondrial EF-Ts (EF-Ts-mt) have been mutated. The abilities of th e resulting EF-Ts-mt derivatives to stimulate the activities of both E . coli and mitochondrial EF-Tu have been tested. Mutation of several r esidues in EF-Ts-mt corresponding to amino acids important for the act ivity off. coli EF-Ts has little or no effect on the activity of the m itochondrial factor, suggesting that these factors may use somewhat di fferent mechanisms to promote guanine nucleotide exchange. In general, mutations that reduce the strength of the interaction between EF-Ts-m t and E. coli EF-Tu increase the ability of EF-Ts-mt to stimulate the activity of the bacterial factor. In contrast, these mutations tend to reduce the ability of EF-Ts-mt to stimulate the activity of EF-Tu(mt) . For example, F19A/I20A and H176A derivatives of EF-Ts-mt are as acti ve as E. coli EF-Ts in simulating E. coli EF-Tu. However, these mutati ons significantly decrease the ability of EF-Ts-mt to stimulate EF-Tu( mt).