ROLE OF THE CONSERVED ASPARTATE AND PHENYLALANINE RESIDUES IN PROKARYOTIC AND MITOCHONDRIAL ELONGATION-FACTOR TS IN GUANINE-NUCLEOTIDE EXCHANGE

The guanine nucleotide exchange reaction catalyzed by elongation facto r Ts is proposed to arise from the intrusion of the side chains of D80 and F81 near the Mg2+ binding site in EF-Tu, D80A and F81A mutants of E. coli EF-Ts were 23-fold less active in promoting GDP exchange with E. coli EF-Tu while the D80AF81A mutant was nearly 10-fold less activ e. The D84 and F85 mutants of EF-Ts(mt) were 5-10-fold less active in stimulating the activity of EF-Tu(mt). The double mutation completely abolished the activity of EF-Ts(mt).