Identification of the RPS10 polypeptide encoded by the mitochondrial genome in Solanum tuberosum: translation initiates at a genomic-encoded AUG and not at a conserved AUG codon created by RNA editing

We have previously reported the identification of a gene encoding ribosomal protein S10 (rps10) in the Solanum tuberosum mitochondrial genome and show n that its transcripts undergo processing in the form of splicing and editi ng. Specific antibodies were raised against recombinant potato RPS10 obtain ed in Escherichia call from the corresponding cDNA. Protein blot analysis r evealed that the RPS10 polypeptide is present in potato mitochondria and is assembled into the mitochondrial ribosome. Potato rps10 mRNA translation m ay initiate at a genomic-encoded AUG codon, or at a downstream in-frame AUG codon which is created by RNA editing and coincides with liverwort and pea initiation codons. A peptide corresponding to the 19 amino acid sequence b etween both putative initiation codons was used to raise antibodies specifi c for the potato RPS10 N-terminal extension. These antibodies were able to recognise a polypeptide of 16 kDa in a potato mitochondrial fraction enrich ed in ribosomes. This molecular mass corresponds to that of the polypeptide detected with antibodies against recombinant RPS10 and is in agreement wit h the molecular weight calculated from the cDNA sequence. These results she lved that potato mitochondrial rps10 gene is expressed at the protein level and that translation initiates at the first genomic-encoded AUG codon. Pot ato RPS10 has an N-terminal extension of unknown function when compared to RPS10 from other organisms.