A ribosomal protein L2 gene is transcribed, spliced, and edited at one site in rice mitochondria

The mitochondrial ribosomal protein L2 gene (rpl2) is coded by two exons of 840 and 669 bp separated by an intron sequence of 1481 bp in the rice mitochondrial genome. The rpl2 gene is located three nucleotides upstream of the ribosomal protein S19 gene (rps19) and both genes are co-transcribed. cDNA sequence analysis identified splicing of the intron sequence from the rpl2 mRNA as well as RNA editing events. The deduced secondary structure of the rpl2 intron sequence shows the characteristic features of a group-II intron. A single RNA editing site is identified in rpl2 and six editing sites in rps19 transcripts. In addition, one editing site is observed in the 3 nucleotide intergenic region. Analysis of individual cDNA clones showed a different extent of RNA editing. The rice rpl2 intron is located at a different site and shows no significant nucleotide sequence similarity with the rpl2 intron of liverwort. However, 60% nucleotide sequence identity is observed between the rice rpl2 intron and the Oenothera nad5 intron in a 234 nucleotide region. The mitochondrial rpl2 sequence is absent from the pea mitochondrial genome and we consequently propose that the mitochondrial RPL2 protein is encoded by a nuclear gene in pea.