Interrupted catalysis: the EF4 (LepA) effect on back-translocation

J Mol Biol. 2010 Mar 5;396(4):1043-52. doi: 10.1016/j.jmb.2009.12.043. Epub 2010 Jan 4.


EF4, although structurally similar to the translocase EF-G, promotes back-translocation of tRNAs on the ribosome and is important for bacterial growth under certain conditions. Here, using a coordinated set of in vitro kinetic measures, including changes in the puromycin reactivity of peptidyl-tRNA and in the fluorescence of labeled tRNAs and mRNA, we elucidate the kinetic mechanism of EF4-catalyzed back-translocation and determine the effects of the translocation inhibitors spectinomycin and viomycin on the process. EF4-dependent back-translocation proceeds from a post-translocation (POST) complex to a pre-translocation (PRE) complex via a four-step kinetic scheme (i.e., POST-->I(1)-->I(2)-->I(3)-->PRE, which is not the simple reverse of translocation). During back-translocation, movements of the tRNA core regions and of mRNA are closely coupled to one another but are sometimes decoupled from movement of the 3'-end of peptidyl-tRNA. EF4 may be thought of as performing an interrupted catalysis of back-translocation, stopping at the formation of I(3) rather than catalyzing the complete process of back-translocation culminating in PRE complex formation. The delay in polypeptide elongation resulting from transient accumulation of I(3) is likely to be important for optimizing functional protein biosynthesis.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Base Sequence
  • Catalysis
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Kinetics
  • Models, Biological
  • Peptide Initiation Factors
  • Puromycin / metabolism
  • RNA, Bacterial / genetics
  • RNA, Bacterial / metabolism
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Transfer, Amino Acyl / genetics
  • RNA, Transfer, Amino Acyl / metabolism
  • Ribosomes / metabolism
  • Spectrometry, Fluorescence
  • Transcriptional Elongation Factors / genetics
  • Transcriptional Elongation Factors / metabolism*


  • Escherichia coli Proteins
  • LepA protein, E coli
  • Peptide Initiation Factors
  • RNA, Bacterial
  • RNA, Messenger
  • RNA, Transfer, Amino Acyl
  • Transcriptional Elongation Factors
  • tRNA, peptidyl-
  • Puromycin