Rat phospholipid-hydroperoxide glutathione peroxidase. cDNA cloning and identification of multiple transcription and translation start sites.

Phospholipid-hydroperoxide glutathione peroxidase (PhGPx) is a selenoenzyme that reduces hydroperoxides of phospholipid, cholesterol, and cholesteryl ester. Previous studies suggested that both the mitochondrial and nonmitochondrial forms of PhGPx are approximately 170 amino acids long. In this study, we isolated a full-length cDNA clone encoding rat testis PhGPx. Based on sequence analysis, the cDNA encodes a protein of 197 amino acids, with translation initiating at AUG61. The additional 27 amino acids at the N terminus contain the features of a mitochondrial targeting sequence. In vitro translation of the full-length PhGPx mRNA initiated predominantly at AUG61. However, translation initiated at AUG141 when AUG61 was deleted. An RNase protection assay was used to map the 5'-ends of PhGPx mRNAs in rat tissues. We identified two major windows of transcription initiation that are tissue-specific. Rat testis predominantly expresses larger transcripts that encode the 197-amino acid protein containing the potential mitochondrial targeting signal. The predominant smaller transcripts in somatic tissues lack AUG61 and encode a 170-amino acid protein, which may represent the nonmitochondrial forms of PhGPx. Our results suggest that the use of alternative transcription and translation start sites determines the subcellular localization of PhGPx in different tissues.