Translation initiation by the c-myc mRNA internal ribosome entry sequence and the poly(A) tail.
Eukaryotic mRNAs possess a poly(A) tail that enhances translation via the (7)mGpppN cap structure or internal ribosome entry sequences (IRESs). Here we address the question of how cellular IRESs recruit the ribosome and how recruitment is augmented by the poly(A) tail. We show that the poly(A) tail enhances 48S complex assembly by the c-myc IRES. Remarkably, this process is independent of the poly(A) binding protein (PABP). Purification of native 48S initiation complexes assembled on c-myc IRES mRNAs and quantitative label-free analysis by liquid chromatography and mass spectrometry directly identify eIFs 2, 3, 4A, 4B, 4GI, and 5 as components of the c-myc IRES 48S initiation complex. Our results demonstrate for the first time that the poly(A) tail augments the initiation step of cellular IRES-driven translation and implicate a distinct subset of translation initiation factors in this process. The mechanistic distinctions from cap-dependent translation may allow specific translational control of the c-myc mRNA and possibly other cellular mRNAs that initiate translation via IRESs.
Thoma
Christian
C
European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany.
Fraterman
Sven
S
Gentzel
Marc
M
Wilm
Matthias
M
Hentze
Matthias W
MW
D002474:Cell-Free System; D006367:HeLa Cells; D006801:Humans; D010442:Peptide Chain Initiation, Translational; D011061:Poly A / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D012315:RNA Caps / Q000378:metabolism
C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D012315:RNA Caps; D011061:Poly A