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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

Two DEAD-Box Proteins May Be Part of RNA-Dependent High-Molecular-Mass Protein Complexes in Arabidopsis Mitochondria^1,[W]

Molekulare Botanik, Universität Ulm, 89069 Ulm, Germany (A.M., S.S.-G., D.K., J.F., S.W., S.B.); and Max-Planck-Institute for Biophysical Chemistry, Bioanalytical Mass Spectrometry Group, D–37077 Goettingen, Germany (M.R., H.U.)

Posttranscriptional processes are important for regulation of gene expression in plant mitochondria. DEAD-box proteins, which form a huge protein family with members from all kingdoms, are fundamental components in virtually all types of processes in RNA metabolism. Two members of this protein family, designated PMH1 and PMH2 (for PUTATIVE MITOCHONDRIAL RNA HELICASE), were analyzed and characterized in mitochondria of Arabidopsis (Arabidopsis thaliana). Green fluorescent protein tagging with N-terminal PMH1 and PMH2 sequences supports the mitochondrial localization of these proteins. Northern experiments, as well as histochemical β-glucuronidase staining of transgenic plants carrying respective promoter:β-glucuronidase fusion constructs, revealed differing transcription patterns for the two genes. In response to cold, however, transcript levels of both genes increased. Immunodetection analyses of mitochondrial protein complexes after two-dimensional blue native/urea SDS-PAGE and after fractionation on sucrose gradients strongly suggest that one or both proteins are part of RNA-dependent complexes. Cold treatment of cell cultures or solubilization of mitochondria in the presence of MgCl₂ favored the detection of high-molecular-mass complexes. This study paves the way for detailed analysis of high-molecular-mass complexes in mitochondria of higher plants.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Stefan Binder (stefan.binder{at}uni-ulm.de).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.108076

^* Corresponding author; e-mail stefan.binder{at}uni-ulm.de.

Received August 24, 2007; accepted October 5, 2007; published October 19, 2007.

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