Figure 1: Processing and expression of Val-tRF. (a) Secondary structure of H. volcanii Val-tRNA with the Val-tRF depicted in red. Arrowheads indicate the processing positions for the four different observed tRF classes (I–IV). Open arrowheads on the Val-tRNA structure indicate the 3′ ends of the tRFs for class I, as well as the analogous positions for the other tRF classes II, and IV. tRFs from classes I, II, and IV are all processed from the 5′ end of mature tRNAs. Filled arrowheads mark the 5′ and 3′ ends of tRFs derived from class III. Northern blot analyses for Val-tRF were performed using (b) total RNA or (c) ribosome-associated RNA. RNA was isolated from unstressed H. volcanii cells (no stress), or cells grown under different permanent environmental stress conditions (ultraviolet stress (UV), high pH (pH↑), 0.9 M NaCl (NaCl), 300 mM MgSO4 (Mg↑)). Arrows indicate the full-length tRNA and the detected processing products. In all panels 5S rRNA served as internal loading control.