Cotranscription of the rpl5-rps14-cob gene cluster in pea mitochondria

Abstract

In pea mitochondria the rpl5, rps14 and cob ORFs are clustered in a unique genomic environment and are cotranscribed into a 4.7-kb primary transcript and several other polycistronic RNAs with sizes between 4.0 and 2.3 kb. All of the larger RNAs terminate at a common 3′ end, 52 nucleotides downstream of the cob gene. Transcription is initiated at a promoter about 1.3 kb upstream of the rpl5 start codon. The promoter sequence 5′-AATAAGAGA-3′ corresponds to the highly conserved 5′-CRTAAGAGA-3′ motif often found in promoters in dicot plants. Functional analysis in a homologous in vitro transcription system showed the pea rpl5 promoter to be active, despite the presence of an altered base in first position of the promoter motif. In Oenothera, in contrast to pea, transcription of the rpl5 gene is driven by a promoter motif that conforms perfectly to the consensus sequence. Double inverted repeats located in the 3′ flanking regions of the rps14 and cob ORFs in pea were investigated with respect to their possible role in defining transcript termini and their potential function in controlling exo- and endonucleolytic processing or transcript stabilization.