Complete Mitochondrial DNA Sequence of Conger myriaster (Teleostei: Anguilliformes): Novel Gene Order for Vertebrate Mitochondrial Genomes and the Phylogenetic Implications for Anguilliform Families

The complete nucleotide sequence of the mitochondrial genome was determined for a conger eel, Conger myriaster (Elopomorpha: Anguilliformes), using a PCR-based approach that employs a long PCR technique and many fish-versatile primers. Although the genome [18,705 base pairs (bp)] contained the same set of 37 mitochondrial genes [two ribosomal RNA (rRNA), 22 transfer RNA (tRNA), and 13 protein-coding genes] as found in other vertebrates, the gene order differed from that recorded for any other vertebrates. In typical vertebrates, the ND6, tRNA^Glu, and tRNA^Pro genes are located between the ND5 gene and the control region, whereas the former three genes, in C. myriaster, have been translocated to a position between the control region and the tRNA^Phe gene that are contiguously located at the 5′ end of the 12S rRNA gene in typical vertebrates. This gene order is similar to the recently reported gene order in four lineages of birds in that the latter lack the ND6, tRNA^Glu, and tRNA^Pro genes between the ND5 gene and the control region; however, the relative position of the tRNA^Pro to the ND6–tRNA^Glu genes in C. myriaster was different from that in the four birds, which presumably resulted from different patterns of tandem duplication of gene regions followed by gene deletions in two distantly related groups of organisms. Sequencing of the ND5–cyt b region in 11 other anguilliform species, representing 11 families, plus one outgroup species, revealed that the same gene order as C. myriaster was shared by another 4 families, belonging to the suborder Congroidei. Although the novel gene orders of four lineages of birds were indicated to have multiple independent origins, phylogenetic analyses using nucleotide sequences from the mitochondrial 12S rRNA and cyt b genes suggested that the novel gene orders of the five anguilliform families had originated in a single ancestral species. Received: 13 July 2000 / Accepted: 30 November 2000     

Relative rates of divergence of spacer and gene sequences within the rDNA region of species in the Triticeae: Implications for the maintenance of homogeneity of a repeated gene family

Summary The relative rates of divergence of 11 regions of the wheat rDNA cloned in pTA250 were estimated by measuring sequence change in 6 Triticum species. The Tm analysis of ³²P probes synthesized from the pTA250 regions and hybridized to DNA from the Triticum species provided an estimate of sequence change relative to T. aestivum. The results revealed a region of 1.2 kb preceding the 18S rRNA gene which was more conserved than the rest of the spacer. In addition the transcribed spacer between the 18S and 26S rRNA genes was shown to be poorly-conserved; the genes, as expected, were highly conserved. A model which proposes RNA as a co-factor in gene conversion is suggested to account for the observations.