RAPESEED MITOCHONDRIAL CCB206, A GENE INVOLVED IN CYTOCHROME-C BIOGENESIS, IS CO-TRANSCRIBED WITH THE NAD3 AND RPS12 GENES - ORGANIZATION, TRANSCRIPTION, AND RNA EDITING OF THE NAD3 RPS12/CCB206 LOCUS/

We describe here the structure and expression of the nad3/rps12/ccb206 locus in the mitochondrial genomes of rapeseed (Brassica napus L.) an d related species. In the rapeseed mitochondrial genome there are thre e tandemly located open reading frames for subunit 3 of NADH dehydroge nase (nad3), the S12 subunit protein of the mitochondrial ribosome (rp s12), and a homologue of one subunit of the ABC-heme transporter (ccb2 06). The gene organization of the nad3/rps12/ccb206 locus found in rap eseed mitochondria is not conserved in Arabidopsis thaliana mitochondr ia, where the ccb206 and nad3/rps12 loci are separated from each other . We show here that the rapeseed gene-organization pattern is also pre sent in other Brassica species, but not in radish, a species very clos ely related to Brassica. Northern hybridization and RT-PCR analyses in dicate that these three mitochondrial genes are possibly co-transcribe d. Ten, seven, and 39 C-to-U RNA editing events occur in the rapeseed nad3, rps12, and ccb206 transcripts, respectively. Finally we show tha t codon position 21 of nad3 is edited in a highly species-specific man ner among related Brassica species, including rapeseed and radish.