A new family of bacterial ribosome hibernation factors has been identified, named Balon, in the cold-adapted bacterium Psychrobacter urativorans. Balon is a distant homologue of the archaeo-eukaryotic translation factor aeRF1 and is found in approximately 20% of bacteria. It binds to ribosomes in an mRNA-independent manner, initiating a new mode of ribosome hibernation that can occur even when ribosomes are actively synthesizing proteins. Balon occupies the ribosomal A site in both vacant and actively translating ribosomes in complex with EF-Tu, highlighting an unexpected role for EF-Tu in the cellular stress response. Unlike typical A-site substrates, Balon binds to ribosomes without requiring mRNA, allowing it to function in a broader range of conditions. Balon is found in many bacteria, including Mycobacteria, and its presence in these organisms suggests a widespread role in ribosome hibernation. Balon's structure is similar to aeRF1 and Pelota, but it lacks key structural features required for their functions. Balon binds to the decoding centre and peptidyl-transferase centre of the ribosome, preventing premature release of nascent peptides. Balon's unique binding mechanism allows it to associate with both vacant and actively translating ribosomes, setting it apart from other hibernation factors. Balon's interaction with EF-Tu is distinct from that of other ribosome hibernation factors, suggesting a different mechanism of ribosome hibernation. Balon's presence in bacteria suggests that it plays a role in ribosome hibernation, which is a conserved mechanism across different organisms. Balon's discovery highlights the importance of studying less common model organisms to uncover new biological mechanisms. Balon's role in ribosome hibernation may have implications for understanding and studying ribosome hibernation in various contexts.A new family of bacterial ribosome hibernation factors has been identified, named Balon, in the cold-adapted bacterium Psychrobacter urativorans. Balon is a distant homologue of the archaeo-eukaryotic translation factor aeRF1 and is found in approximately 20% of bacteria. It binds to ribosomes in an mRNA-independent manner, initiating a new mode of ribosome hibernation that can occur even when ribosomes are actively synthesizing proteins. Balon occupies the ribosomal A site in both vacant and actively translating ribosomes in complex with EF-Tu, highlighting an unexpected role for EF-Tu in the cellular stress response. Unlike typical A-site substrates, Balon binds to ribosomes without requiring mRNA, allowing it to function in a broader range of conditions. Balon is found in many bacteria, including Mycobacteria, and its presence in these organisms suggests a widespread role in ribosome hibernation. Balon's structure is similar to aeRF1 and Pelota, but it lacks key structural features required for their functions. Balon binds to the decoding centre and peptidyl-transferase centre of the ribosome, preventing premature release of nascent peptides. Balon's unique binding mechanism allows it to associate with both vacant and actively translating ribosomes, setting it apart from other hibernation factors. Balon's interaction with EF-Tu is distinct from that of other ribosome hibernation factors, suggesting a different mechanism of ribosome hibernation. Balon's presence in bacteria suggests that it plays a role in ribosome hibernation, which is a conserved mechanism across different organisms. Balon's discovery highlights the importance of studying less common model organisms to uncover new biological mechanisms. Balon's role in ribosome hibernation may have implications for understanding and studying ribosome hibernation in various contexts.