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The pioneer translation initiation complex is functionally distinct from but structurally overlaps with the
Shang-Yi Chiu1, Fabrice Lejeune, Aparna C Ranganathan
1Department of Biochemistry and Biophysics, School of Medicine and Dentistry, University of Rochester, Rochester, New York 14642, USA.
Genes & Development
|April 3, 2004
Summary
The pioneer round of translation, distinct from steady-state translation, involves cap-binding protein (CBP)80-bound mRNA and is not inhibited by 4E-BP1. This early translation process utilizes key factors like poly(A)-binding protein (PABP)1 and eIF2alpha.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Most cellular protein production relies on eukaryotic translation initiation factor (eIF)4E-bound mRNA.
- Nonsense-mediated mRNA decay (NMD) studies reveal that cap-binding protein (CBP)80-bound mRNA, a precursor to eIF4E-bound mRNA, can undergo translation during a pioneer round.
Purpose of the Study:
- To investigate the distinct mechanisms of pioneer round translation compared to steady-state translation.
- To determine the role of 4E-BP1 in regulating pioneer round translation.
- To identify protein factors involved in both translation modes.
Main Methods:
- Assessing pioneer round translation by measuring NMD.
- Investigating the effect of 4E-BP1 on pioneer translation.
- Co-immunoprecipitation of translation factors with CBP80 and eIF4E.
- Analyzing polysome profiles to compare mRNA translation efficiency.
Main Results:
- The pioneer round of translation is not inhibited by 4E-BP1, differentiating it from steady-state translation.
- Key translation factors including eIF4GI, poly(A)-binding protein (PABP)1, eIF3, eIF4AI, and eIF2alpha associate with both CBP80 and eIF4E.
- PABP1 and eIF2alpha play roles in pioneer round translation, as evidenced by the inhibitory effects of PABP-interacting protein 2 and inactive eIF2alpha on NMD.
- CBP80-bound mRNAs show less efficient translation than eIF4E-bound mRNAs based on polysome profiles.
Conclusions:
- Pioneer round translation is a distinct mechanism from steady-state translation, notably unaffected by 4E-BP1.
- Shared protein factors participate in both translation initiation pathways.
- CBP80-bound mRNAs are translated less efficiently than eIF4E-bound mRNAs during the pioneer round.