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A poly(A) binding protein functions in the chloroplast as a message-specific translation factor
1Department of Cell Biology and The Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Summary
Researchers identified RB47, a poly(A) binding protein, as crucial for regulating psbA mRNA translation in Chlamydomonas reinhardtii chloroplasts. This finding reveals a eukaryotic-like translation factor in chloroplasts, expanding the known roles of poly(A) binding proteins.
Area of Science:
- Molecular Biology
- Plant Science
- Biochemistry
Background:
- Specific proteins bind the 5' untranslated region (UTR) of Chlamydomonas reinhardtii chloroplast psbA mRNA.
- This binding correlates with light-regulated translational activation of the psbA message.
Purpose of the Study:
- To isolate and identify the main psbA RNA binding protein.
- To investigate the role of this protein in chloroplast gene expression.
Main Methods:
- cDNA isolation and sequencing for RB47.
- In vitro translation and chloroplast import assays.
- Protein expression and purification from E. coli for binding studies.
Main Results:
- The main psbA RNA binding protein, RB47, was identified as a member of the poly(A) binding protein family.
- RB47 precursor protein is efficiently imported and processed in chloroplasts.
- Recombinant RB47 binds the psbA 5' UTR with high affinity and specificity.
Conclusions:
- A normally cytoplasmic translation factor (RB47) functions within the chloroplast.
- This suggests eukaryotic-like translation initiation factors regulate key chloroplast mRNAs.
- Poly(A) binding proteins may have broader roles in translation regulation than previously understood.