title: Elongation factor 4 (EF4/LepA) accelerates protein synthesis at increased Mg2+ concentrations.
abstract: Elongation factor 4 (EF4) is one of the most conserved proteins present in bacteria as well as in mitochondria and chloroplasts of eukaryotes. Although EF4 has the unique ability to catalyze the back-translocation reaction on posttranslocation state ribosomes, the physiological role of EF4 remains unclear. Here we demonstrate that EF4 is stored at the membrane of Escherichia coli cells and released into the cytoplasm upon conditions of high ionic strength or low temperature. Under such conditions, wild-type E. coli cells overgrow mutant cells lacking the EF4 gene within 5-10 generations. Elevated intracellular Mg(2+) concentrations or low temperature retard bacterial growth and inhibit protein synthesis, probably because of formation of aberrant elongating ribosomal states. We suggest that EF4 binds to these stuck ribosomes and remobilizes them, consistent with the EF4-dependent enhancement (fivefold) in protein synthesis observed under these unfavorable conditions. The strong selective advantage conferred by the presence of EF4 at high intracellular ionic strength or low temperatures explains the ubiquitous distribution and high conservation of EF4.
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, AG Ribosomen, Ihnestrasse 73, 14195 Berlin, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Pech
authors.forename: Zhala
authors.initials: Z
authors.lastname: Karim
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Madoka
authors.initials: M
authors.lastname: Kitakawa
authors.forename: Yan
authors.initials: Y
authors.lastname: Qin
authors.forename: Knud H
authors.initials: KH
authors.lastname: Nierhaus
mesh_terms: D004926:Escherichia coli / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000378:metabolism* / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D009994:Osmolar Concentration; D010448:Peptide Initiation Factors; D014176:Protein Biosynthesis / Q000235:genetics*; D021381:Protein Transport; D012270:Ribosomes / Q000473:pathology; D013696:Temperature; D035602:Transcriptional Elongation Factors / Q000378:metabolism* / Q000502:physiology
chemical_list: D029968:Escherichia coli Proteins; C515651:LepA protein, E coli; D010448:Peptide Initiation Factors; D035602:Transcriptional Elongation Factors; D008274:Magnesium