Sequence analysis of dolphin ferritin H and L subunits and possible iron-dependent translational control of dolphin ferritin gene

Sequence analyses of cetacean ferritin H and L subunits were performed by direct sequencing of polymerase chain reaction (PCR) fragments from cDNAs generated via reverse transcription-PCR of leukocyte total RNA prepared from blood samples of six different dolphin species (Pseudorca crassidens, Lagenorhynchus obliquidens, Grampus griseus, Globicephala macrorhynchus, Tursiops truncatus, and Delphinapterus leucas). The putative iron-responsive element sequence in the 5'-untranslated region of the six different dolphin species was revealed by direct sequencing of PCR fragments obtained using leukocyte genomic DNA.Dolphin H and L subunits consist of 182 and 174 amino acids, respectively, and amino acid sequence identities of ferritin subunits among these dolphins are highly conserved (H: 99–100%, (99→98) ; L: 98–100%). The conserved 28 bp IRE sequence was located -144 bp upstream from the initiation codon in the six different dolphin species.These results indicate that six different dolphin species have conserved ferritin sequences, and suggest that these genes are iron-dependently expressed.Ferritin is a ubiquitous iron storage protein found in all living organisms [1-3]. It also functions to segregate iron in a non-toxic form to prevent iron-catalyzed reactive oxygen species production [3-7]. Mammalian tissue ferritins consist of two functionally different subunits, termed as H (heavy chain, heart-type) and L (light chain, liver-type), and a central cavity accommodating up to 4,500 iron atoms [1,8]. A novel mitochondrial ferritin has also found in humans and rodents, and their ferritins only consist of a novel H-type subunit with 80% identity to their H subunits [9]. The H subunit plays a crucial role in incorporating iron through its ferroxidase activity [10,11]. The L subunit lacks ferroxidase activity, but is involved in iron nucleation to allow more iron to be sequestered [8,11-13].The H and L subunits of many mammalian ferritins have been sequenced; each subunit s