Figure 6.

Possible involvement of ribosomes in tasiRNA biogenesis from pri-TAS2: a model. i, An 80S ribosome is formed at the initiation codons of ORF3 on pri-TAS2 and moves in the 3′ direction. In steady state, a few ribosomes bind to pri-TAS2. ii, A miR173-programmed RISC cleaves a pri-TAS2. iii, A ribosome that is translating the ORF3 encounters the complex containing the RISC and SGS3 near the cleavage site, and then stalls at this point. If translation initiation continues, multiple ribosomes become stacked on the 5′ cleavage fragment, followed by SDE5 action on the cleavage fragments. iv, RDR6 converts the ribosome-free 3′ cleavage fragment into a dsRNA. ORF3 and ORFs longer than 12 nt are shown as red and blue bars, respectively. Where two coding regions of different frames overlap, only upstream ORFs are shown.