Cloning and characterization of the genes for ribosomal proteins L10 and L12 from Synechocystis Sp. PCC 6803: comparison of gene clustering pattern and protein sequence homology between cyanobacteria and chloroplasts.

The endosymbiont theory proposes that chloroplasts have originated from ancestral cyanobacteria through a process of engulfment and subsequent symbiotic adaptation. The molecular data for testing this theory have mainly been the nucleotide sequence of rRNAs and of photosystem component genes. In order to provide additional data in this area, we have isolated genomic clones of Synechocystis DNA containing the ribosomal protein gene cluster rplJL. The nucleotide sequence of this cluster and flanking regions was determined and the derived amino acid sequences were compared to the available homologous sequences from other eubacteria and chloroplasts. In Escherichia coli these two genes are part of a larger cluster, i.e., rplKAJL-rpoBC. In Synechocystis, the genes for the RNA polymerase subunit (rpoBC) are shown to be widely separated from the r-protein genes. The Synechocystis gene arrangement is similar to that in the chloroplast system, where the rpoBC1C2 and rplKAJL clusters are separated and located in two cell compartments, the chloroplast and the nucleus, respectively.