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Conservation and diversity of eukaryotic translation initiation factor eIF3
K Asano1, T G Kinzy, W C Merrick
1Department of Biological Chemistry, School of Medicine, University of California, Davis 95616, USA.
The Journal of Biological Chemistry
|January 10, 1997
Summary
This study identifies and characterizes human translation initiation factor eIF3 subunits p110 and p36, revealing both conserved and diverse components compared to yeast eIF3.
Area of Science:
- Molecular Biology
- Cell Biology
- Protein Biochemistry
Background:
- The eukaryotic translation initiation factor 3 (eIF3) is a large complex crucial for protein synthesis initiation.
- eIF3 interacts with the 40S ribosome, facilitating the recruitment of messenger RNA (mRNA) and initiator methionyl-tRNA.
- Understanding the composition of eIF3, particularly its subunits, is vital for elucidating translation regulation.
Purpose of the Study:
- To clone and characterize the human cDNAs encoding two subunits of eIF3: p110 and p36.
- To investigate the presence and localization of these subunits within the eIF3 complex.
- To compare the human eIF3 subunits with their yeast counterparts to identify conserved and divergent features.
Main Methods:
- Cloning and sequencing of human cDNAs for eIF3 subunits p110 and p36.
- Polyacrylamide gel electrophoresis (PAGE) to analyze eIF3 subunit composition.
- Sequence homology analysis comparing human and yeast protein sequences.
- Cellular localization studies using 40S ribosomes.
- Co-immunoprecipitation assays to confirm subunit association within eIF3.
Main Results:
- Human cDNAs for eIF3 subunits p110 and p36 were successfully cloned and characterized.
- The p110 subunit shows 31% identity to the yeast protein Nip1, while p36 is a WD40 repeat protein, 46% identical to yeast p39 and identical to TRIP-1.
- Subunits p116, p110, and p36 were found to localize on 40S ribosomes and co-immunoprecipitate with the eIF3 p170 subunit, confirming their integral role in the complex.
- While p36 and p116 have yeast homologs, the p110 homolog (Nip1) was not detected in yeast eIF3 preparations.
Conclusions:
- Human eIF3 contains integral subunits p110, p116, and p36, which are essential components of the translation initiation machinery.
- The study highlights both conserved (p36, p116 homologs) and divergent (p110/Nip1) aspects of eIF3 composition between yeast and humans.
- These findings contribute to a deeper understanding of the structural diversity and evolutionary conservation of translation initiation factors across eukaryotes.