| Mammalian mitochondria maintain their double-stranded circular genome in DNA-protein complexes known as nucleoids, similar to bacteria. While bacterial and yeast mitochondrial nucleoids have been studied more extensively, much is unknown about the protein composition and events that occur at mammalian mitochondrial nucleoids. Recent work has identified many novel mitochondrial nucleoid proteins by mass spectrometry, however the functions of many of these proteins are not well understood. One of the interesting proteins identified by mass spectrometry is RNMTL1, a putative RNA methyltransferase. A search for related mitochondrial proteins in proteomic databases revealed MRM1 and MRM2 as potential RNA methyltransferases as well. The work reported in this thesis includes an initial characterization of the three novel rRNA methyltransferase proteins. We provide data on the subcellular localization of these proteins and the macromolecular complexes in which they exist. We have slightly focused more on RNMTL1, since neither RNMTL1 nor any known homologues have previously been characterized, and provide data on its protein interacting partners. We also provide evidence that RNMTL1 has an important role in mammalian mitochondrial translation. In addition, we have assigned the three methyltransferases to their specific substrate sites on the mitochondrial large ribosomal subunit rRNA. MRM1, MRM2 and RNMTL1 methylate the 2'-O-ribose of G1145 , U1369 and G1370, respectively. These methyltransferases are also likely involved in mitochondrial ribosome assembly and/or stability. |
