Eukaryotic mitochondria are equipped with a com-plete thioredoxin system, composed of thioredoxin and thioredoxin reductase, which has been implicated in the protection against the reactive oxygen intermedi-ates generated during the respiratory process in this organelle. Like its cytosolic counterpart, mammalian mitochondrial thioredoxin reductase is a homodimeric selenoprotein. We report here the genomic organiza-tion of the mouse mitochondrial thioredoxin gene (TrxR2) that spans 53 kb and consists of 18 exons ranging from 20 to 210 bp. All splicing sites conformed to the GT/AG rule with the exon-intron boundaries located exactly at the same position as the human TrxR2 gene, the only mammalian mitochondrial thio-redoxin reductase gene whose genomic structure has been elucidated to date. In addition, we have identified a novel mRNA splicing variant lacking intron 14 re-sulting in a protein subunit with a shorter interface domain. This new splicing variant provides a frame-work for further analysis of this important enzyme as its predicted homodimeric conformation can now be expanded to a putative heterodimeric structure as well as a small subunit homodimer with the obvious impli-cations at the regulatory level.

Keywords: Thiored, Mitochondria, Alternative Splicing, Mouse