Conserved Function of Drg GTPases in Promoting Protein Synthesis in Stalled Ribosomes

Maintaining proper protein homeostasis is essential for cell physiology. The ribosome and GTPases, which are two of the most ancient and critical cellular molecules, are central players in protein synthesis and its regulation. Here we report the discovery of a new general translation factor that targets stalled ribosomes and promotes protein synthesis in an evolutionarily conserved manner. We show that the essential bacterial Obg GTPases are distant homologs of eukaryotic and archaeal Drg proteins and serve critical roles in promoting efficient protein translation in stalled ribosomes. Through in vivo characterization, including cross-species complementation of cells where ribosomes are induced to stall by addition of either the antibiotic anisomycin or exogenous mRNA harboring a long poly(A) sequence, we demonstrate that a conserved function of Drg proteins is to alleviate ribosomal stalling during translation. Our data show that bacterial Obg rescues stalled ribosomes in both Saccharomyces cerevisiae and human cells lacking endogenous Drgs, as does supplementation of the respective endogenous Drg proteins from yeast and human cells. Furthermore, the presence of ObgE and GTP stimulates peptidyl transfer, the key catalytic function of the ribosome, suggesting a possible molecular mechanism of this GTPase to enhance translation in stalled ribosomes. This discovery shows that the Drg protein is a new general translation factor that directly affords cells from the three domains of life a new form of translation regulation.