SPLICING AND EDITING OF RPS10 TRANSCRIPTS IN POTATO MITOCHONDRIA

The structure and expression of the potato mitochondrial gene rps10, e ncoding ribosomal protein S10, has been characterized. The RPS10 polyp eptide of 129 amino acids is encoded by two exons of 307 bp and 80 bp respectively, which are separated by a 774-bp class-II intron. Editing of the complete rps10 coding region was studied by sequence analysis of spliced cDNAs. Four C residues are edited into U, resulting in the creation of a putative translational initiation codon, a new stop codo n which eliminated ten carboxy-terminal residues, and two additional a mino-acid alterations. All these changes increase the similarity betwe en the potato and liverwort polypeptides. One additional C-to-U RNA ed iting event, observed in the intron sequence of unspliced cDNAs, impro ves the stability of the secondary structure in stem I (i) of domain I and may thus be required for the splicing reaction. All spliced cDNAs , and most unspliced cDNAs, were completely edited, suggesting that ed iting is an early step of rps10 mRNA processing and precedes splicing. Earlier work on potato rps10 (Zanlungo et al. 1994) is now known to c omprise only a partial analysis of the gene, since the short downstrea m exon was not identified.