Transcription of potato mitochondrial 26S rRNA is initiated at its mature 5' end.

Transcription initiation sites in plant mitochondria can be located by in vitro capping of primary 5' transcript termini. Direct sequencing of a cap-labelled mitochondrial RNA from potato shows its sequence to be identical to the 5' terminal part of the 26S rRNA. Primer extension analysis indicates the mature 5' end to be the sole detectable 5' transcript terminus. In potato mitochondria the mature 5' end of the 26S rRNA is thus created by transcription initiation without any further 5' processing. The nucleotide sequence surrounding this transcription initiation site shows only limited similarity to other putative promoter sequences from dicot plant mitochondria suggesting the possibility that divergent RNA polymerases, and/or transcription initiation factors, are present in plant mitochondria.