Mutation analysis of the functional role of amino acid residues in domain IV of elongation factor G

The polymerase chain reaction was used to produce seven variants of Thermus thermophilus elongation factor G (EF-G) with mutations Glu494Ile, Gly495Asp, Lys496Ile, His509Leu, Lys564Ile, and Tyr568Lys, localized in the beta-sheet of domain IV, and mutation Gly553Asp, residing in the loop between domains III and IV. It was demonstrated that only the Lys496Ile mutation, located close to the beginning of loop 501-504, influenced the efficiency of translocation in the presence of mutant EF-G. Functional analysis of all the known mutations of domain IV showed that only mutations in loops 501-504 and 573-578, localized to the tip of domain IV, had a pronounced effect on the translocation activity of EF-G. Upon the interaction of EF-G with ribosomes, these loops are the closest to the decoding center, formed in the structure of the 16S RNA in the 30S subunit. The role of EF-G and its domain IV in ribosomal translocation is discussed.