title: The conserved protein EF4 (LepA) modulates the elongation cycle of protein synthesis.
abstract: EF4 (LepA), a strongly conserved protein, is important for bacterial growth and functional protein biosynthesis under certain conditions and is quite similar structurally to the translocase EF-G. The elongation cycle in protein synthesis is characterized by ribosome oscillation between pretranslocation (PRE) and posttranslocation (POST) complexes. Here, using ensemble single turnover and equilibrium experiments, as well as single molecule FRET measurements, we demonstrate that EF4 can compete with EF-G for binding to the PRE complex. Such EF4 binding results in formation of a complex, denoted X(3), that effectively sequesters a catalytically active ribosome, leading to a transient inhibition of elongation that provides a mechanism for optimization of functional protein synthesis. Earlier [Liu H, et al. (2010) J Mol Biol 396:1043-1052] we demonstrated that EF4 also reacts with POST complex, leading to the formation of a complex, I(3), that appears to be identical with X(3). Our present results strongly suggest that PRE complex is the principal target of EF4 action on translation, rather than POST complex as had been previously supposed.
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Hanqing
authors.initials: H
authors.lastname: Liu
authors.forename: Chunlai
authors.initials: C
authors.lastname: Chen
authors.forename: Haibo
authors.initials: H
authors.lastname: Zhang
authors.forename: Jaskiran
authors.initials: J
authors.lastname: Kaur
authors.forename: Yale E
authors.initials: YE
authors.lastname: Goldman
authors.forename: Barry S
authors.initials: BS
authors.lastname: Cooperman
mesh_terms: D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D005453:Fluorescence; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D020653:Peptide Elongation Factor G / Q000378:metabolism; D010448:Peptide Initiation Factors; D014176:Protein Biosynthesis / Q000502:physiology*; D035602:Transcriptional Elongation Factors / Q000378:metabolism / Q000502:physiology*
chemical_list: D029968:Escherichia coli Proteins; C515651:LepA protein, E coli; D020653:Peptide Elongation Factor G; D010448:Peptide Initiation Factors; D035602:Transcriptional Elongation Factors; D008274:Magnesium