sRNA associated to mature tRNAs. (A) tRNA structure and the four types of sRNA fragments associated to tRNAs (tRFs) as observed from the sequencing of the different libraries. Variations in fragment lengths are represented in light gray. (B) Expression validation of selected tRFs by Northern blotting. Total RNA was extracted from cell cultures grown under iron starvation (−Fe) and normal condition (+Fe) in Low Light. Northern blots were hybridized using oligonucleotides recognizing the small tRF products. M, microRNA Marker (New England Biolabs, USA).