THE COMPLETE NUCLEOTIDE-SEQUENCE OF THE MITOCHONDRIAL-DNA GENOME OF THE RAINBOW-TROUT, ONCORHYNCHUS-MYKISS

The complete nucleotide sequence of the mitochondrial DNA of the rainb ow trout, Onchorynchus mykiss, has been determined. The total length o f the molecule is 16,660 bp. The rainbow trout mitochondrial DNA has t he same organization described in eutherian mammals, the clawed frog ( Xenopus laevis), and the two fish species, Oriental stream leach (Cros sotoma lacustre) and carp (Cyprinus cat-pie). Alignment and comparison of the deduced amino acid sequences of the 13 proteins encoded by rai nbow trout and other vertebrate mitochondrial genomes allowed us to es timate that COI is the most conserved mitochondrial subunit (amino aci d identity ranging from 85.6% to 94.8%) whereas ATPase 8 is the most v ariable one (amino acid identity ranging from 30.8% to 70.4%). Putativ e secondary structures for the 22 tRNAs found in the molecule are give n along with an extensive comparison of tRNA sequences among represent ative species of each major group of vertebrates. In this sense, an un usual cloverleaf structure for the tRNA(ser(AGY)) is proposed. A stem- loop structure inferred for the origin of the L-strand replication (O- L) and the presence of a large polycytidine tract in the O-L loop is d escribed. The existence of this stretch instead of the usual T-rich se quence reported so far in mammal mtDNAs is explained in terms of a les s-strict template dependence of the RNA primase involved in the initia tion of L-strand replication.