TOBACCO CHLOROPLAST RIBOSOMES CONTAIN A HOMOLOG OF ESCHERICHIA-COLI RIBOSOMAL-PROTEIN L28

The genes for ribosomal proteins L28 and L33 constitute an operon (rpmBG) in E. coli, but in plant chloroplasts L33 is encoded by DNA and L28 seems to be encoded by the nuclear genome. A 15 kDa protein was isolated from the 50 S subunit of tobacco chloroplast ribosomes and its N-terminal amino acid sequence was determined. A cDNA for this protein was cloned and analyzed. The cDNA encodes a 151 amino acid protein consisting of a predicted transit-peptide of 74 amino acids and a mature protein of 77 amino acids. The mature protein is homologous to E. coli L28, hence we named it chloroplast L28 (CL28). This is the first report on the presence of an E. coli L28-like protein in another organism.