Activities of Ligatin and MCT-1/DENR in eukaryotic translation initiation and ribosomal recycling

Genes Dev. 2010 Aug 15;24(16):1787-801. doi: 10.1101/gad.1957510.

Abstract

Eukaryotic translation initiation begins with ribosomal recruitment of aminoacylated initiator tRNA (Met-tRNA(Met)(i)) by eukaryotic initiation factor eIF2. In cooperation with eIF3, eIF1, and eIF1A, Met-tRNA(Met)(i)/eIF2/GTP binds to 40S subunits yielding 43S preinitiation complexes that attach to the 5'-terminal region of mRNAs and then scan to the initiation codon to form 48S initiation complexes with established codon-anticodon base-pairing. Stress-activated phosphorylation of eIF2alpha reduces the level of active eIF2, globally inhibiting translation. However, translation of several viral mRNAs, including Sindbis virus (SV) 26S mRNA and mRNAs containing hepatitis C virus (HCV)-like IRESs, is wholly or partially resistant to inhibition by eIF2 phosphorylation, despite requiring Met-tRNA(Met)(i). Here we report the identification of related proteins that individually (Ligatin) or together (the oncogene MCT-1 and DENR, which are homologous to N-terminal and C-terminal regions of Ligatin, respectively) promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes, if attachment of 40S subunits to the mRNA places the initiation codon directly in the P site, as on HCV-like IRESs and, as we show here, SV 26S mRNA. In addition to their role in initiation, Ligatin and MCT-1/DENR can promote release of deacylated tRNA and mRNA from recycled 40S subunits after ABCE1-mediated dissociation of post-termination ribosomes.

Publication types

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

MeSH terms

  • Animals
  • Eukaryotic Initiation Factors / metabolism*
  • Hepacivirus / metabolism
  • Membrane Proteins / metabolism*
  • Monocarboxylic Acid Transporters / metabolism*
  • Protein Biosynthesis / physiology
  • RNA, Messenger / metabolism
  • RNA, Transfer / metabolism
  • RNA, Viral / metabolism
  • Rabbits
  • Ribosome Subunits, Small, Eukaryotic / metabolism
  • Ribosomes / metabolism*
  • Sindbis Virus / metabolism
  • Viral Proteins / metabolism

Substances

  • Eukaryotic Initiation Factors
  • Membrane Proteins
  • Monocarboxylic Acid Transporters
  • RNA, Messenger
  • RNA, Viral
  • Viral Proteins
  • ligatin
  • RNA, Transfer