Transferring the ribosomal protein S10 gene from the mitochondrion to the nucleus in rice.

The mitochondrial genome contains only a few genes and most mitochondrial proteins seem to be encoded by the nuclear genome, suggesting a gene transfer event from the mitochondrion to the nucleus during evolution. However, little is known about the details of such gene transfer events. We report that a gene for mitochondrial ribosomal protein S10 (rps10) has been transferred to the nucleus in rice. The rps10 is encoded by the mitochondrial genome in potato and pea, but is absent from the rice mitochondrial genome and has been transferred to the nucleus. Interestingly, there are two rps10 genes in the rice nucleus and their transcript abundance differs. Protein blot analysis detected the RPS10 protein in rice mitochondria, although the RPS10 has no N-terminal presequence for protein targeting to mitochondria. This result suggests that targeting information is encoded in their internal region. Genomic sequence analysis indicated that each rps10 gene has an intron in the 5′ untranslated region and that their intron sequences are homologous to each other. This result strongly suggested that a duplication event occurred after the transfer of the rps10 gene to the nucleus.