The Pisum sativum mitochondrial gene encoding cytochrome oxidase subunit I has an unusual transcription pattern

We report the transcriptional analysis of the mitochondrial (mt) gene encoding cytochrome oxidase subunit I (COXI). A probe made from the protein-coding region of the pea coxI gene hybridized to four RNA transcripts, two of which are much larger than necessary to encode the COXI polypeptide. The RNA hybridization was repeated with a series of sequential probes made from the 5'-untranslated region. The results of these experiments indicated that all four transcripts initiate between 2.8 and 2.1 kb upstream from the protein-coding region. Furthermore, the pattern of hybridization to these sequential probes was unusual, suggesting that introns are spliced out of the 5'-transcribed, but untranslated, region. A sequence located within one of the sequential probes is repeated elsewhere in the pea mt genome. Transcript termini were mapped for the 5' and 3' ends and putative regulatory sequences were located.