Article

A mitochondrial rRNA dimethyladenosine methyltransferase in Arabidopsis

Institut für Biologie/Genetik, Humboldt-Universität, Chausseestr. 117, 10115 Berlin, Germany.
The Plant Journal (Impact Factor: 6.82). 11/2009; 61(4):558-69. DOI: 10.1111/j.1365-313X.2009.04079.x
Source: PubMed

ABSTRACT S-adenosyl-L-methionine-dependent rRNA dimethylases mediate the methylation of two conserved adenosines near the 3' end of the rRNA in the small ribosomal subunits of bacteria, archaea and eukaryotes. Proteins related to this family of dimethylases play an essential role as transcription factors (mtTFBs) in fungal and animal mitochondria. Human mitochondrial rRNA is methylated and human mitochondria contain two related mtTFBs, one proposed to act as rRNA dimethylase, the other as transcription factor. The nuclear genome of Arabidopsis thaliana encodes three dimethylase/mtTFB-like proteins, one of which, Dim1B, is shown here to be imported into mitochondria. Transcription initiation by mitochondrial RNA polymerases appears not to be stimulated by Dim1B in vitro. In line with this finding, phylogenetic analyses revealed Dim1B to be more closely related to a group of eukaryotic non-mitochondrial rRNA dimethylases (Dim1s) than to fungal and animal mtTFBs. We found that Dim1B was capable of substituting the E. coli rRNA dimethylase activity of KsgA. Moreover, we observed methylation of the conserved adenines in the 18S rRNA of Arabidopsis mitochondria; this modification was not detectable in a mutant lacking Dim1B. These data provide evidence: (i) for rRNA methylation in Arabidopsis mitochondria; and (ii) that Dim1B is the enzyme catalyzing this process.

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Available from: Uwe Richter, Oct 16, 2014
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    • "In contrast, three TFB2M-like genes were found in the Arabidopsis nuclear genome, one of which coded for a mitochondrial protein named DIM1B (Richter et al., 2010). Unlike TFB2M, DIM1B was found to function as a mitochondrial rRNA dimethyl transferase rather than transcriptional cofactor, and phylogenetic analyses placed DIM1B and its plant orthologues next to nucleolar rRNA dimethyl transferases rather than yeast Mtf1 or mammalian TFB2M (Richter et al., 2010). "
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    • "The plant mitoribosome contains three rRNA molecules encoded in the mitochondrial DNA, 26S and 5S for the LSU, and 18S for the SSU. The rRNAs undergo several important posttranscriptional modifications (pseudouridylation and methylation ; Bonen, 2004), and an rRNA methyltransferase required for the dimethylation of two conserved adenines in the mitochondrial 18S rRNA of Arabidopsis was characterized (Richter et al., 2010). "
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    • "Confocal imaging revealed that DIM1A-GFP was localized primarily in root cell nuclei, most strongly in subnuclear regions presumed to be the nucleolus (Figures 6A to 6C). This result is consistent with recent work showing nucleolar localization of DIM1A-GFP transiently expressed in Arabidopsis protoplasts (Richter et al., 2010) and predominantly nucleolar localization of Dim1p in yeast (Lafontaine et al., 1998). At an organ-wide level, DIM1A-GFP was observed in all tissue types in the developing root (Figure 6F). "
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