Complete Sequence of the Mitochondrial DNA of the Rhodophyte Chondrus crispus(Gigartinales). Gene Content and Genome Organization

Abstract

The complete nucleotide sequence of the circular mitochondrial (mt) DNA from the red alga Chondrus crispuswas determined (25, 836 nucleotides, A+T content 72.1%). Fifty one genes were identified. They include genes encoding three subunits of the cytochrome oxidase ( cox1 to 3), apocytochrome b ( cob), seven subunits of the NADH dehydrogenase complex ( nad1to 6, nad4L), two ATPase subunits ( atp6and atp9), three ribosomal RNAs ( rrn5, srnand Irn), 23 tRNAs and four ribosomal proteins ( rps3, rps11, rps12and rpl16). Two subunits of the succinate dehydrogenase complex ( sdhBand sdhC), usually found on nuclear genomes, are also located on the mtDNA of C. crispus.One group IIb intron is inserted in the tRNA IIegene. Six potentially functional open reading frames were identified, four of them having counterparts among green plant mtDNAs. The use of a modified genetic code and the absence of RNA editing, previously reported for the cox3gene, appears as a general characteristic of this molecule. Mitochondrial genes are encoded on both DNA strands, in two opposite major transcriptional directions, suggesting the existence of two main transcriptional units. Two long and stable stem-loops were identified in intergenic regions, which are believed to be involved with transcription and replication. The main structural features of this genome are compared with the overall organization of mtDNAs and are discussed in view of the evolution of mitochondria.