Bacterial IF2's N-terminal IDR drives cold-induced phase separation and promotes fitness during cold stress.

Translation initiation factor 2 (IF2) plays an essential role in bacterial cells by delivering the fMet-tRNA(fMet) to the ribosome pre-initiation complex. IF2 is known to have an N-terminal disordered region which is present across bacterial species, yet its function is not fully understood. Deletion of the IDR in E. coli showed no phenotypes at normal growth temperature (37°C); however, this IDR was found to be required for growth at cold temperatures (15°C). Since large IDRs can drive phase separation of various RNA binding proteins into biomolecular condensates, we investigated whether E. coli IF2 could phase separate. We discovered that IF2's N-terminal IDR drives phase separation in E. coli and C. crescentus, suggesting that IF2 condensation is a conserved property. Finally, using E. coli, we found that the IDR strongly drives phase separation in the cold, suggesting IF2 condensates promote fitness during cold stress.