Stall no more at polyproline stretches with the translation elongation factors EF‐P and IF‐5A

Summary Synthesis of polyproline proteins leads to translation arrest. To overcome this ribosome stalling effect, bacteria depend on a specialized translation elongation factor P ( EF‐P ), being orthologous and functionally identical to eukaryotic/archaeal elongation factor e/a IF ‐5 A (recently renamed ‘ EF 5’). EF ‐ P binds to the stalled ribosome between the peptidyl‐t RNA binding and t RNA ‐exiting sites, and stimulates peptidyl‐transferase activity, thus allowing translation to resume. In their active form, both EF ‐ P and e/a IF ‐5 A are post‐translationally modified at a positively charged residue, which protrudes toward the peptidyl‐transferase center when bound to the ribosome. While archaeal and eukaryotic IF ‐5 A strictly depend on (deoxy‐) hypusination (hypusinylation) of a conserved lysine, bacteria have evolved diverse analogous modification strategies to activate EF ‐ P . In E scherichia coli and S almonella enterica a lysine is extended by β‐lysinylation and subsequently hydroxylated, whereas in P seudomonas aeruginosa and S hewanella oneidensis an arginine in the equivalent position is rhamnosylated. Inactivation of EF ‐ P , or the corresponding modification systems, reduces not only bacterial fitness, but also impairs virulence. Here, we review the function of EF ‐ P and IF ‐5 A and their unusual posttranslational protein modifications.