Mitochondria are made up of proteins encoded by the nuclear genome as well as its own genome, thus requiring both cytosolic as well as its own translation apparatus for its biogenesis. The proper biogeneis of mitochodria is critical as 1 in 5,000 humans suffers from a mitochondrial disease and a number of these diseases are due to defects in the mitochondrial translation apparatus. Importance of mitochondrial translation apparatus can be estimated with the fact that approximately 25% of the mitochondrial proteome is involved in the establishment and the maintenance of the mitochondrial protein synthesis apparatus and mitochondrial DNA. Mitochondria utilize dedicated ribosome molecules that are encoded by a set of nuclear genes distinct from those coding for its cytosolic counterpart. Mitochondrial ribosomes have reduced RNA content and a higher protein content giving rise to numerous mitochondrial specific proteins conserved from lower eukaryotes to humans. Ribosome biogenesis is a multi-step process aided by assembly factors including GTPases which are thought to utilize energy released upon GTP hydrolysis to promote its biogenesis activity. Mtg3p, is a nuclear encoded mitochondrial protein that is conserved from yeast to humans and is a member of YawG/YlqF family of circularly permuted GTPases. Deletion of MTG3 leads to defects in utilization of glycerol as the sole carbon source and accumulate 15S rRNA precursors. We have shown Mtg3p associates with the 37S small subunit of the mitochondrial ribosome in a salt dependent manner. Cells harboring mtg3ts mutants have aberrant large to small ribosomal subunit ratio consistent with a role in mitochondrial ribosome biogenesis. Our studies also indicate that Mtg3p requires guanine nucleotide binding as well as hydrolysis to carry out its in vivo function at a late step during mitochondrial ribosome biogenesis perhaps just prior to association with mRNA to form 74S monosome. In addition, we have isolated spontaneous suppressors for Δmtg3ρ+ and have determined them to be due to second-site mutations in the mitochondrial genome. We will be presenting our studies aimed at identifying the molecular complexes that Mtg3p is associated with, domains of Mtg3p that are essential for its in vivo function and the downstream partners/processes that it likely controls.