Structural Insights into the Mammalian Late-Stage Initiation Complexes

Cell Rep. 2020 Apr 7;31(1):107497. doi: 10.1016/j.celrep.2020.03.061.

Abstract

In higher eukaryotes, the mRNA sequence in the direct vicinity of the start codon, called the Kozak sequence (CRCCaugG, where R is a purine), is known to influence the rate of the initiation process. However, the molecular basis underlying its role remains poorly understood. Here, we present the cryoelectron microscopy (cryo-EM) structures of mammalian late-stage 48S initiation complexes (LS48S ICs) in the presence of two different native mRNA sequences, β-globin and histone 4, at overall resolution of 3 and 3.5 Å, respectively. Our high-resolution structures unravel key interactions from the mRNA to eukaryotic initiation factors (eIFs): 1A, 2, 3, 18S rRNA, and several 40S ribosomal proteins. In addition, we are able to study the structural role of ABCE1 in the formation of native 48S ICs. Our results reveal a comprehensive map of ribosome/eIF-mRNA and ribosome/eIF-tRNA interactions and suggest the impact of mRNA sequence on the structure of the LS48S IC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / genetics
  • ATP-Binding Cassette Transporters / metabolism
  • Animals
  • Codon, Initiator / genetics
  • Codon, Initiator / ultrastructure
  • Cryoelectron Microscopy / methods
  • Enhancer Elements, Genetic / genetics
  • Eukaryotic Initiation Factor-1 / genetics
  • Eukaryotic Initiation Factor-1 / metabolism
  • Eukaryotic Initiation Factor-2 / genetics
  • Eukaryotic Initiation Factor-2 / metabolism
  • Eukaryotic Initiation Factor-3 / genetics
  • Eukaryotic Initiation Factor-3 / metabolism
  • Eukaryotic Initiation Factors / metabolism*
  • Eukaryotic Initiation Factors / ultrastructure*
  • Humans
  • Mice
  • Peptide Chain Initiation, Translational
  • Protein Biosynthesis
  • RNA, Messenger / metabolism
  • RNA, Ribosomal, 18S / genetics
  • RNA, Ribosomal, 18S / metabolism
  • RNA, Transfer / metabolism
  • Ribosomal Proteins / metabolism
  • Ribosomes / metabolism
  • Transcription Initiation, Genetic / physiology*
  • beta-Globins / genetics
  • beta-Globins / ultrastructure

Substances

  • ATP-Binding Cassette Transporters
  • Codon, Initiator
  • Eukaryotic Initiation Factor-1
  • Eukaryotic Initiation Factor-2
  • Eukaryotic Initiation Factor-3
  • Eukaryotic Initiation Factors
  • RNA, Messenger
  • RNA, Ribosomal, 18S
  • Ribosomal Proteins
  • beta-Globins
  • eukaryotic peptide initiation factor-1A
  • RNA, Transfer