RAT PHOSPHOLIPID-HYDROPEROXIDE GLUTATHIONE-PEROXIDASE - CDNA CLONING AND IDENTIFICATION OF MULTIPLE TRANSCRIPTION AND TRANSLATION START SITES

Phospholipid-hydroperoxide glutathione peroxidase (PhGPx) is a selenoe nzyme that reduces hydroperoxides of phospholipid, cholesterol, and ch olesteryl ester, Previous studies suggested that both the mitochondria l and nonmitochondrial forms of PhGPx are similar to 170 amino acids l ong, In this study, we isolated a full-length cDNA clone encoding rat testis PhGPx, Based on sequence analysis, the cDNA encodes a protein o f 197 amino acids, with translation initiating at AUG(61). The additio nal 27 amino acids at the N terminus contain the features of a mitocho ndrial targeting sequence. In vitro translation of the full-length PhG Px mRNA initiated predominantly at AUG(61). However, translation initi ated at AUG(141) when AUG(61) was deleted, An RNase protection assay w as used to map the 5'-ends of PhGPx mRNAs in rat tissues, We identifie d two major windows of transcription initiation that are tissue specif ic. Rat testis predominantly expresses larger transcripts that encode the 197-amino acid protein containing the potential mitochondrial targ eting signal, The predominant smaller transcripts in somatic tissues l ack AUG(61) and encode a 170-amino acid protein, which may represent t he nonmitochondrial forms of PhGPx, Our results suggest that the use o f alternative transcription and translation start sites determines the subcellular localization of PhGPx in different tissues.