Steinar Daae Johansen

By Tor Erik Jørgensen and Steinar Daae Johansen

Vertebrate mitochondrial genomes are highly conserved in structure, gene content, and function. Most sequenced mitochondrial genomes represent bony fishes, and that of the Atlantic cod (Gadus morhua) is the best characterized among the fishes. In addition to the well-characterized 37 canonical gene products encoded by vertebrate mitochondrial genomes, new classes of gene products representing peptides and noncoding RNAs have been discovered. The Atlantic cod encodes at least two peptides (MOTS-c and humanin (HN)), two long noncoding RNAs (lncCR-L and lncCR-H), and a number of small RNAs. Here, we review recent research in the Atlantic cod focusing on putative mitochondrial-derived peptides, the mitochondrial transcriptome, and noncoding RNAs.

Part of the book: Mitochondrial DNA

By Steinar Daae Johansen and Åse Emblem

Hexacoral mitochondrial genomes are highly economically organized and vertebrate-like in size, structure, and gene content. A hallmark, however, is the presence of group I introns interrupting essential oxidative phosphorylation (OxPhos) genes. Two genes, encoding NADH dehydrogenase subunit 5 (ND5) and cytochrome c oxidase subunit I (COI), are interrupted with introns. The ND5 intron, located at position 717, is obligatory in all hexacoral specimens investigated. The ND5-717 intron is a giant-sized intron that carries several canonical OxPhos genes. Different modes of splicing appear to apply for the ND5-717 intron, including conventional cis-splicing, backsplicing, and trans-splicing. Three distinct versions of hexacoral COI introns are noted at genic positions 884, 867, and 720. The COI introns are of the mobile-type, carrying homing endonuclease genes (HEGs). Some COI-884 intron HEGs are highly expressed as in-frame COI exon fusions, while the expression of COI-867 intron HEGs appear repressed. We discuss biological roles of hexacoral mitochondrial ND5 and COI introns and suggest that the ND5-717 intron has gained new regulatory functions beyond self-splicing.

Part of the book: Advances in the Studies of the Benthic Zone