Cloning and characterization of the ribosomal protein genes in the spc operon of a prokaryotic endosymbiont of the pea aphid, Acyrthosiphon kondoi.

To correlate a prokaryotic endosymbiont in the pea aphid, Acyrthosiphon kondoi, with the endosymbionts in related aphid species as well as with free-living bacteria and subcellular organelles, and to study the mode of its gene expression within aphid cells, we have cloned and characterized the genes encoding ribosomal proteins S3, L16, L29, S17, L14, L24, L5, S14, S8, L6, L18, S5, L30, L15 and secretion protein Y (Sec Y) from the S10 and spc ribosomal protein gene operons of this endosymbiont. The organization of these genes is identical to that in Escherichia coli, and their nucleotide sequences are highly similar (87% identity) to the corresponding E. coli genes. They are much less similar to the corresponding chloroplast and mitochondrial genes. The guanine plus cytosine G+C content of the genes of the A. kondoi endosymbiont is much higher than those of the endosymbionts in related aphid species reported so far. It appears either that the A. kondoi endosymbiont is derived from an ancestral bacterium different from those in other aphids or that its G+C content increased in a relatively short time after the evolutionary divergence of its host.