A Conserved Obg-type GTPase sustains protein synthesis and its physiological roles in eukaryotic cells
Translation is regulated both temporally and spatially to ensure that proteins are synthesized at the correct time and delivered to the proper subcellular location. Temporary slowing or halting of ribosomal movement along an mRNA, a physiological pausing, allows cells to coordinate protein production with internal cues and external signals. However, how cells distinguish such constructive pauses from harmful pathological stalls remains a fundamental unresolved question in molecular biology. Here, we report that a ribosome-binding GTPase (Rbg in yeast, and so-called Developmentally Regulated GTP-binding (Drg) in human) promotes protein biosynthesis in halted ribosomes in an evolutionarily conserved manner. We show that the essential bacterial Obg GTPase rescues cell growth and translation in Saccharomyces cerevisiae and human cells lacking their endogenous Rbg/Drg proteins in a GTPase-dependent manner. Furthermore, Obg enhances puromycin incorporation into stalled ribosomes in a manner requiring GTP hydrolysis. We reason that Rbg/Drg proteins act to prevent premature engagement of ribosome-associated quality-control or stress-response pathways. Under physiological conditions, proteomic analyses of Rbg1-bound ribosomes in yeast reveal that Rbg GTPases associate with ribosomes translating proteins essential for diverse functions, including those of the nucleus, ER, Golgi, mitochondria, and protein transport pathways. Finally, loss of even one of the two eukaryotic Rbg/Drg paralogs impedes cell-cycle progression, disrupts DNA replication, and compromises mitochondrial function. Together, these findings suggest that Rbg/Drg proteins enable cells across different domains of life to protect physiological ribosomal pauses, revealing a previously unrecognized layer of regulation in gene expression. Significance StatementHow cells distinguish productive ribosomal pauses from harmful stalls remains unclear. We identify a ribosome-binding GTPase--Rbg in yeast and Drg in humans--as a conserved regulator that protects physiological pauses and sustains protein synthesis. Remarkably, bacterial Obg functionally substitutes for eukaryotic Rbg/Drg in both yeast and human cells, revealing deep evolutionary conservation of this mechanism. Our data show that Obg promotes continued peptide-bond formation in a GTPase-dependent manner. Positioned near the ribosomal GTPase-associated center, these GTPases are also poised to compete with stringent-response and stress-activation factors that trigger translation shutdown. Together, the findings suggest that translation is controlled not only by GTPases that drive protein synthesis forward but also by Rbg/Drg GTPases that protect the catalytic cycle against premature arrest.