The 5'-7-methylguanosine cap on eukaryotic mRNAs serves both to stimulate canonical translation initiation and to block an alternative pathway.
Translational control is frequently exerted at the stage of mRNA recruitment to the initiating ribosome. We have reconstituted mRNA recruitment to the 43S preinitiation complex (PIC) using purified S. cerevisiae components. We show that eIF3 and the eIF4 factors not only stabilize binding of mRNA to the PIC, they also dramatically increase the rate of recruitment. Although capped mRNAs require eIF3 and the eIF4 factors for efficient recruitment to the PIC, uncapped mRNAs can be recruited in the presence of eIF3 alone. The cap strongly inhibits this alternative recruitment pathway, imposing a requirement for the eIF4 factors for rapid and stable binding of natural mRNA. Our data suggest that the 5' cap serves as both a positive and negative element in mRNA recruitment, promoting initiation in the presence of the canonical group of mRNA handling factors while preventing binding to the ribosome via an aberrant, alternative pathway requiring only eIF3.
Mitchell
Sarah F
SF
Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Walker
Sarah E
SE
Algire
Mikkel A
MA
Park
Eun-Hee
EH
Hinnebusch
Alan G
AG
Lorsch
Jon R
JR
D002474:Cell-Free System / Q000378:metabolism; D039621:Eukaryotic Initiation Factor-3 / Q000378:metabolism; D039601:Eukaryotic Initiation Factor-4A / Q000378:metabolism; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D039562:Eukaryotic Initiation Factor-4F / Q000378:metabolism; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D039642:Eukaryotic Initiation Factors / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D006151:Guanosine / Q000031:analogs & derivatives* / Q000378:metabolism; D007700:Kinetics; D009690:Nucleic Acid Conformation; D010442:Peptide Chain Initiation, Translational / Q000502:physiology*; D011485:Protein Binding / Q000502:physiology; D054730:Protein Interaction Domains and Motifs / Q000502:physiology; D012314:RNA Cap Analogs / Q000502:physiology; D012315:RNA Caps / Q000378:metabolism*; D012331:RNA, Fungal / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000235:genetics; D054682:Ribosome Subunits, Small, Eukaryotic / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics
D039621:Eukaryotic Initiation Factor-3; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D039642:Eukaryotic Initiation Factors; D012314:RNA Cap Analogs; D012315:RNA Caps; D012331:RNA, Fungal; C472563:RPL41 protein, S cerevisiae; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C031799:eIF-4B; D006151:Guanosine; C016578:7-methylguanosine; C017516:7-methylguanosine triphosphate; D039601:Eukaryotic Initiation Factor-4A