Transcription initiation sites for sorghum mitochondrial atp9 are positioned immediately 3' to trnfM

Sorghum mitochondrial atp9 is polymorphic among male-sterile cytoplasms, but each cytoplasm is characterized by a major 650 nt transcript, regardless of fertility status. The gene is positioned 323 bp 3' to trnfM. Primer extension revealed multiple atp9 5' transcript termini, distributed from +1 to +28 3' to trnfM; the termini could be labeled with polynucleotide kinase, suggesting that they result from the maturation of trnfM. Guanylyltransferase experiments, however, showed that four of the termini were capable. The juxtaposition of a putative promoter 3' to trnfM results in a unique atp9 transcript population consisting of primary and processed transcripts.