FUNCTIONAL ANALYSIS OF TWO CONSERVED REGIONS OF ESCHERICHIA COLI ELONGATION FACTOR G AS STUDIED BY SITE-DIRECTED MUTAGENESIS
Elongation factor G (EF-G) catalyzes the translocation step of protein biosynthesis. The function of two conserved regions of E. coli EF-G, that are located at the interfaces between domains, was explored by mutating four highly conserved residues, R127, Q128, G461 and E462.Analysis of R127 mutants revealed that R127 is involved in ribosome binding. No other aspect of the EF-G cycle was significantly affected by mutation of this arginine. Q128 is involved in ribosome-dependent GTP hydrolysis. As a consequence of its defect in ribosome-dependent GTPase activity, the Q128 mutants displayed a reduced specific activity in a turnover protein synthesis assay and increased dissociation from the ribosome. Destabilization of the switch II helix by mutation of the Q128 residue might explain the defects observed in the Q128 mutants. G461 was shown to be essential for the function of EF-G. Mutation of the G461 residue caused severe defects in the ribosome-dependent GTPase activity, reduced GTP binding, reduced binding to the ribosome and almost no protein synthesis. E462 was involved in the hydrolysis of GTP. Mutants of E462 were functional in all other aspects of the EF-G cycle and had similar protein synthesis activity as wild-type EF-G.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:protein synthesis ef g gtpase translation
Date of Publication:01/01/2002