The S. pombe and D. discoideum strains used in this study are shown in Supplementary Table S2. S. pombe strains were cultured in standard full medium (YES) (5 g/l yeast extract, 30 g/l glucose, 250 mg/l adenine, 250 mg/l histidine, 250 mg/l leucine, 250 mg/l uracil, 250 mg/l lysine). Gene knockouts in S. pombe and D. discoideum were obtained by homologous recombination, and correct knockout was verified by polymerase chain reaction (PCR) analysis (24 (link)–26 (link)). Primer sequences are listed in Supplementary Tables S3 and S4. All Dictyostelium strains used in this study are derived from strain Ax2–214. Cells were cultured in HL5 medium (Formedium) containing ampicillin (50 μg/ml), amphotericin-B (0.25 μg/ml), penicillin/ streptomycin (100 μg/ml) and chloramphenicol (34 μg/ml). Where required, antibiotics for selection (blasticidin S and/or G418 sulfate, 10 μg/ml each) were added. For RNA preparation, cells were grown shaking under continuous light at 22°C up to a cell density of 2 × 106 cells/ml. Queuine isolated from bovine amniotic fluid was added to S. pombe cultures in YES medium at 0.03 μM. D. discoideum cultures were grown for at least four days with 0.1 μM queuine, kindly provided by Klaus Reuter, Marburg (27 (link)).