A YEAST SPECIFIC INSERTION AMIDST OBG FOLD IS CRITICAL FOR THE MITOCHONDRIAL FUNCTION OF M tg 2 p IN SACCHAROMYCES CEREVISIAE

Protein expression in mitochondria is carried out by ribosomes that are distinct from their cytosolic counterpart. Mitochondrial ribosomes are made of individual proteins having distinct lineages: those with clear bacterial orthologues, those conserved in eukaryotes only and proteins that are species specific. MTG2 is the mitochondrial member of the universally conserved Obg family of GTPases in Saccharomyces cerevisiae which associates with and regulates mitochondrial large ribosomal subunit assembly. In this study we demonstrate that MTG2, in addition to the universally conserved OBG and GTPase domains, has an essential yeast specific insertion domain positioned within the N terminal OBG fold. Cells expressing mtg2Δ 201-294 , deleted for the insertion domain are not able to support cellular respiration. In addition, we show that largestretches of amino acids can be inserted into MTG2 at the end of the yeast specific insertion domain and the OBG fold without perturbing its cellular functions, consistent with the insertion domain folding into a species specific protein binding platform. Keywords : mitochondrial ribosome; Mtg2p/Obg