TRANSCRIPTION INITIATION AND RNA PROCESSING IN THE MITOCHONDRIA OF THE RED ALGA CHONDRUS-CRISPUS - CONVERGENCE IN THE EVOLUTION OF TRANSCRIPTION MECHANISMS IN MITOCHONDRIA

The mitochondrial DNA (mt DNA) of the red alga Chondrus crispus is sho wn to be transcribed into two large RNA molecules. These primary trans cripts are cleaved once, at the level of a tRNA, then the resulting pr oducts are processed via multiple maturation events into either mono- or poly-cistronic RNAs. Transcripts were detected for all genes and op en reading frames, except for rps11 and orf172. For both transcription units the initiation of transcription was mapped by in vitro RNA capp ing and primer extension experiments within inverse repeated sequences at the north pole of the molecule. Consistent with primer extension m apping, putative promoter motifs sharing significant similarities with both chicken and Xenopus mitochondrial promoters were found in the C. crispus mitochondrial genome. Altogether C. crispus mitochondrial DNA appears to be transcribed as animal mtDNA is, suggesting that transcr iption mechanisms in mitochondria are dependent on the overall organiz ation of the mitochondrial genome irrespective of the eukaryotic phylo geny. (C) 1998 Academic Press.