A nuclear gene encoding the beta subunit of the mitochondrial ATP synthase in Nicotiana plumbaginifolia

The beta subunit of the mitochondrial ATP synthase in Nicotiana plumbaginifolia is encoded by two nuclear genes, atp2-1 and atp2-2, which are both expressed. The complete nucleotide sequence of atp2-1 has been determined. It contains eight introns ranging from 88 to 1453 bp. The last intron contains a putative insertion element (Inp), of 812 bp bordered by 35-bp inverted repeats which share an 11-bp homology with Agrobacterium tumefaciens T-DNA borders. Sequences homologous to Inp are present in multiple copies in the N. plumbaginifolia and the N. tabacum genome but not in more distant species. The atp2-1 encoded polypeptide is highly homologous to beta subunits from other ATP synthases but it contains an extension at the N terminus which is probably involved in mitochondrial targeting. A sequence homology between exon 4 of atp2-1 and exon 1 of the human ras genes suggests a common ancestral origin for these exons.