The C-terminal region of mitochondrial single-subunit RNA polymerases contains species-specific determinants for maintenance of intact mitochondrial genomes

Thomas Lisowsky¹^*, Detlef Wilkens¹, Torsten Stein², Boris Hedtke³, Thomas Börner³, and Andreas Weihe³

¹ Botanisches Institut, Heinrich-Heine-Universität Düsseldorf, Universitätsstrabe 1, D-40225 Düsseldorf, Germany
² Department of Pathology, University of Glasgow, Western Infirmary, Glasgow, G11 6NT, UK
³ Institut für Biologie, Humboldt Universität, Chausseestr. 117, D-10115 Berlin, Germany

^* Corresponding author. E-mail address: lisowsky{at}uni-duesseldorf.de.

Functional conservation of mitochondrial RNA polymerases was investigated in vivo by heterologous complementation studies in yeast. It turned out that neither the full-length mitochondrial RNA polymerase of Arabidopsis thaliana, nor a set of chimeric fusion constructs from plant and yeast RNA polymerases can substitute for the yeast mitochondrial core enzyme Rpo41p when expressed in ${Delta}$ rpo41 yeast mutants. Mitochondria from mutant cells, expressing the heterologous mitochondrial RNA polymerases, were devoid of any mitochondrial genomes. One important exception was observed when the carboxyl-terminal domain of Rpo41p was exchanged with its plant counterpart. Although this fusion protein could not restore respiratory function, stable maintenance of mitochondrial petite genomes ( ${rho}$ -) -was supported. A carboxyl-terminally truncated Rpo41p exhibited a comparable activity, in spite of the fact that it was found to be transcriptionally inactive. Finally, we tested the carboxyl-terminal domain for complementation in trans. For this purpose the last 377 amino acid residues of yeast mitochondrial Rpo41p were fused to its mitochondrial import sequence. Co-expression of this fusion protein with C-terminally truncated Rpo41p complemented the ${Delta}$ rpo41 defect. These data reveal the importance of the carboxyl-terminal extension of Rpo41p for stable maintenance of intact mitochondrial genomes and for distinct species-specific intra-molecular protein-protein interactions.