A poly(A) binding protein functions in the chloroplast as a message-specific translation factor

A poly(A) binding protein functions in the chloroplast as a message-specific translation factor

Department of Cell Biology and The Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037

Communicated by Roger N. Beachy, The Scripps Research Institute, La Jolla, CA (received for review December 4, 1997)

Abstract

High-affinity binding of a set of proteins with specificity for the 5′ untranslated region (UTR) of the Chlamydomonas reinhardtii chloroplast psbA mRNA correlates with light-regulated translational activation of this message. We have isolated a cDNA encoding the main psbA RNA binding protein, RB47, and identified this protein as a member of the poly(A) binding protein family. Poly(A) binding proteins are a family of eukaryotic, cytoplasmic proteins thought to bind poly(A) tails of mRNAs and play a role in translational regulation. In vitro translation of RNA transcribed from the RB47 cDNA produces a precursor protein that is efficiently transported into the chloroplast and processed to the mature 47-kDa protein. RB47 expressed and purified from Escherichia coli binds to the psbA 5′ UTR with similar specificity and affinity as RB47 isolated from C. reinhardtii chloroplasts. The identification of a normally cytoplasmic translation factor in the chloroplast suggests that the prokaryotic-like chloroplast translation machinery utilizes a eukaryotic-like initiation factor to regulate the translation of a key chloroplast mRNA. These data also suggest that poly(A) binding proteins may play a wider role in translation regulation than previously appreciated.

Footnotes

↵ * Present address: Program in Developmental Genetics, The Skirball Institute, New York University Medical Center, 540 First Avenue, 4th Floor, New York, NY 10016.
↵ † Present address: Dept. of Biological Sciences, California State University, Fullerton, CA 92834-6850.
↵ ‡ Present address: Department of Plant Genetics, The Weizmann Institute of Science, Rehovot, 76100, Israel.
↵ § To whom reprint requests should be addressed. e-mail: mayfield{at}scripps.edu.
Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. AF043297).
ABBREVIATIONS:

IVT,

in vitro translation;

PABP,

poly(A) binding protein;

RRM,

RNA recognition motif;

UTR,

untranslated region