Chloroplast Genes Coding for Ribosomal Proteins in Land Plants

Abstract

Chloroplast ribosomes in land plants are 70S in size similar to prokaryotic ribosomes and contain 23S, 16S, 5S and 4.5S rRNAs and about 60 ribosomal proteins (for reviews see Palmer 1985, Sugiura 19 89). All the rRNAs are known to be encoded in the chloroplast genome. Analyses of the synthesis of ribosomal proteins in isolated chloroplasts have shown that the chloroplast genome encodes about one-third of the ribosomal proteins (Eneas-Filho et al 1981, Dorne et al 1984b, Posno et al 1984). The rest of chloroplast ribosomal proteins are thought to be encoded in the nuclear genome. The electrophoretic patterns and molecular weight frequency distributions of the proteins of higher plant chloroplast ribosomes are quite similar to those of the Escherichia coli ribosomes (Mache et al. 1980, Capel & Bourque et al 1981). Determination of the primary structure of ribosomal protein L12 from spinach chloroplasts (Bartsch et al 1982) and immunological studies (Dorne et al 1984a, Bartsch 1985) showed also the similarity of chloroplast and E. coli ribosomal proteins. These observations led us to search for chloroplast ribosomal protein genes through their homology with E. coli counterparts.