title: The function of conserved amino acid residues adjacent to the effector domain in elongation factor G.
abstract: Bacterial elongation factor G (EF-G) physically associates with translocation-competent ribosomes and facilitates transition to the subsequent codon through the coordinate binding and hydrolysis of GTP. In order to investigate the amino acid positions necessary for EF-G functions, a series of mutations were constructed in the EF-G structural gene (fusA) of Escherichia coli, specifically at positions flanking the effector domain. A mutated allele was isolated in which the wild-type sequence from codons 29 to 47 ("EFG2947") was replaced with a sequence encoding 28 amino acids from ribosomal protein S7. This mutated gene was unable to complement a fusAts strain when supplied in trans at the nonpermissive temperature. In vitro biochemical analysis demonstrated that nucleotide crosslinking was unaffected in EFG2947, while ribosome binding appeared to be completely abolished. A series of point mutations created within this region, encoding L30A, Y32A, H37A, and K38A were shown to give rise to fully functional proteins, suggesting that side chains of these individual residues are not essential for EF-G function. A sixth mutant, E41A, was found to inefficiently rescue growth in a fusAts background, and was also unable to bind ribosomes normally in vitro. In contrast E41Q could restore growth at the nonpermissive temperature. These results can be explained within the context of a three-dimensional model for the effector region of EF-G. This model indicates that the effector domain contains a negative potential field that may be important for ribosome binding.
authors.affiliation: School of Microbiology and Immunology, University of New South Wales, Sydney, Australia.
authors.forename: J D
authors.initials: JD
authors.lastname: Sharer
authors.forename: H
authors.initials: H
authors.lastname: Koosha
authors.forename: W B
authors.initials: WB
authors.lastname: Church
authors.forename: P E
authors.initials: PE
authors.lastname: March
mesh_terms: D000595:Amino Acid Sequence; D017124:Conserved Sequence; D003432:Cross-Linking Reagents / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics / Q000254:growth & development; D006160:Guanosine Triphosphate / Q000737:chemistry / Q000528:radiation effects; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020653:Peptide Elongation Factor G / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012270:Ribosomes / Q000378:metabolism; D055672:Static Electricity; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D020653:Peptide Elongation Factor G; D006160:Guanosine Triphosphate