Transcript map of oppositely oriented pea mitochondrial genes encoding the alpha-subunit and the subunit 9 of F1F0-ATPase complex.

The atpA gene of pea mitochondria coding for the alpha-subunit of F1F0-ATPase (ATP synthase) is carried on four types of genomic segments generated by recombination, and two of these segments contain the atp9 gene coding for the subunit 9 of F1F0ATPase in the 5'-upstream region of atpA in an opposite orientation. The atpA and atp9 genes were separated by a spacer of 2112 bp, which does not contain any open reading frame. Pea mitochondria contained at least four atpA transcripts of 4.5, 2.7, 2.3, and 1.8 kb and at least three atp9 transcripts of 1.35, 0.6, and 0.4 kb. Mapping of these transcripts by northern blot hybridization, primer extension, and S1-nuclease mapping indicated that multiple transcripts of atpA differ in their length both at their 5'- and 3'-termini. On the other hand, three transcripts of atp9 differed in their length only at their 5'-termini. It was found that the 5'-terminal sequence of the 4.5-kb transcript of atpA is complementary to the 5'-terminal part of the 1.35- and 0.6-kb transcripts of atp9 for 705 and 4 nucleotides, respectively.