Figure 1.
A selection cycle. Color coding: T7-promoter (17 nt) - dark red, 5'-primer (19 nt) - red, random region (50 nt) - black, HDV ribozyme (87 nt) - blue. [α 32P G] pool RNA has 69 nt; HDV ribozyme (67 nt) is distinct because it can be 3′-elongated to 87 nt without change in reactivity. Self-cleavage results in 2′,3′-cyclic phosphate at the 3′-end of transcript RNA, that must be opened and dephosphorylated.