Mitochondrial plasmid DNAs of broad bean: nucleotide sequences, complex secondary structures, and transcription.

Three circular plasmid DNA molecules of 1704, 1695 and 1476 nucleotide pairs from broad bean mitochondria (mt-plasmids 1-3) have been sequenced. Within a highly homologous segment of mt-plasmid 1 and 2 are found a series of six directly repeated, inverted repeat sequences, separated by unique sequences. Mt-plasmid 3 contains a series of four inverted repeat sequences, unrelated to the inverted repeat sequences of mt-plasmids 1 and 2. Two RNA molecules of about 440 and 320 nucleotides that are complementary to mt-plasmid 2 were detected. Mapping of 5' and 3' termini of these complementary RNA molecules indicated that all transcription from mt-plasmid 2 occurs within a 441 nucleotide region of the molecule. Evidence for transcription of mt-plasmids 1 and 3 was not found.