Transcription of yeast and plant mtDNA
The mtDNA in yeast is 78kbp and that in higher plants (master circle) is 200-240kbp, in contrast to a small (16-17kbp) mitochondrial genome in vertebrates. In yeast, mitochondrial genes are separated by extensive AT-rich non-coding spacer sequences; a bulk of mtDNA in higher plants is also non-coding. A 5S rRNA gene is a novel gene found only in plant mtDNA. In mtDNA of both yeast and higher plants, there are multiple transcription units, each with a separate promoter (unlike vertebrate mtDNA having a single promoter on each strand (LSP and HSP).
In higher plants, only 30%-70% of mtDNA is known to be transcribed, which gives rise to 20-30 polypeptides, 3 rRNA species and 15-20 tRNAs. Currently promoters of transcription units in higher plants mtDNA are being discovered. The RNA polymerases and the transcription factors associated with transcription of plant mtDNA, will be isolated and characterized during 1990s.