Analyses of the Nuclear Genes for Components of the Chloroplast Genetic System

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The components of the chloroplast genetic system are encoded both in the nuclear and chloroplast genomes. The present purpose is to analyzed the nuclear genes (including cDNAs) for the components.1) We isolated the 50S ribosomal subunit, fractionated its proteins and determined their N-terminal amino acid sequences. The 14 kd protein sequence matched that deduced from ORF55 located in tobacco chloroplast DNA and hence we designated it as rp132 based on its homology to the E. coli L32.2) We isolated three proteins (cp28, cp31, cp33) from a tobacco chloroplast lysate using an ssDNA affinity column and determined their N-terminal amino acid sequences. We then obtained their cDNA clones, determined their DNA sequences and found the presence of two RNA-binding domains in all three proteins. Invitro RNA-binding assays revealed that they are ribonucleoproteins.3) We isolated tobacco chloroplast EF-Tu and its cDNAs, and analyzed their primary structures. There are two distinct genes for chloroplast EF-Tu in N. Sylvestris.