Transcription initiation sites in mitochondria of Oenothera berteriana

Abstract

Toward the identification of promoter structures in dicot plant mitochondria, transcription initiation sites were localized by in vitro capping of mitochondrial RNAs from Oenothera berteriana. By this approach at least 15 initiation sites are detectable in the genome. Primary 5'-transcript termini were determined for coxII, atpA, and an 18 S rRNA precursor. Alignment of the sequences surrounding the transcript termini defines a conserved sequence block of 29 nucleotides between positions -20 and +9. A core of 9 nucleotides between positions -7 and +2 (5'-CRTAaGaGA-3') is conserved with soybean transcription initiation sites. All transcripts analyzed begin with the underlined GA-dinucleotide. Transcription initiation of these protein coding and ribosomal RNA genes at similar sequence elements suggests common binding specificities of the RNA polymerase or its cofactors for both types of genes. The putative promoter consensus motif for dicots is very different from monocot mitochondrial promoter sequences. Only the 5'-CRTA-3' tetranucleotide is conserved between both plant groups.