Identification of a plastid-specific ribosomal protein in the 30 S subunit of chloroplast ribosomes and isolation of the cDNA clone encoding its cytoplasmic precursor.

C H Johnson,V Kruft,A R Subramanian

doi:10.1016/s0021-9258(19)38228-6

Abstract

We describe the isolation and characterization of a chloroplast ribosomal protein and a clone of its cDNA. This protein has no homology to any Escherichia coli ribosomal protein or to any known proteins. Due to this novel finding we propose it be called PSrp-1, i.e. a plastid-specific ribosomal protein. The precursor form of PSrp-1, deduced from the cDNA sequence, is 302-amino acid residues long. The mature PSrp-1, identified by amino-terminal sequencing, is a protein of 236 residues. The NH2-terminal 66 amino acids form the transit peptide that targets PSrp-1 into the chloroplast. We show that PSrp-1 is a protein of the chloroplast 30 S ribosomal subunit by Western blotting and sequencing the excised protein after two-dimensional gel electrophoresis. The possible evolutionary origin of PSrp-1 from the nucleated host cell of the endosymbiont theory is discussed.

Highlights

We describe the isolation and characterization of a chloroplast ribosomal protein and a clone of its cDNA
We show that PSrp-1 is a protein of the chloroplast 30 S ribosomal subunit by Western blotting and sequencing the excised protein after two-dimensional gel electrophoresis
The results have indicated a larger number of polypeptides than in the E. coli ribosome, suggesting that the chloroplast ribosome has apparently evolved to a more complex state than its eubacterial counterpart

Summary

Introduction

We describe the isolation and characterization of a chloroplast ribosomal protein and a clone of its cDNA. The precursor form of PSrp-1, deduced from the cDNA sequence, is 302-amino acid residues long.

Results

Conclusion