Structural organization of a nuclear gene for the alpha-subunit of the bovine mitochondrial ATP synthase complex

Abstract

The structural organization of an expressed bovine gene (ATPA1) that encodes an isoform of the alpha-subunit of the mitochondrial F0F1 ATP synthase was determined. The gene extends over 10 kilobase-pairs and is divided into 12 exons. The first exon encodes the 5' untranslated region and approximately one-half of the presequence that targets this protein to the mitochondrion. The remainder of the presequence, together with three amino acids of the mature protein, are encoded by exon 2. Primer extension and nuclease protection analyses revealed multiple sites of transcription initiation. The 5' flanking region of the ATPA1 gene can drive the transcription of a reporter gene in an orientation-dependent manner. This promoter region contains several sequence elements which might play an important role in regulating the expression of this gene, including possible TATA and CCAAT boxes, putative Sp1-binding sites, and sequences resembling AP-1, AP-2, AP-4 and cAMP-responsive elements. The ATPA1 gene also contains sequences homologous to several motifs that are shared among some nuclear genes encoding mitochondrial proteins. These include Mt1, Mt3, Mt4, a respiratory enhancer, and NRF-2 sites. Tissue-specific differences in the ATPA1 mRNA levels were observed with high levels found in skeletal muscle and heart, and lower levels in other tissues.