Figure 5.

A manganese-dependent ribozyme in the zipcode of β-actin mRNA. (A) The predicted secondary structure of the zipcode element in the 3′-UTR of β-actin mRNA (52). An arrow marks the site of manganese-dependent cleavage. (B) Zipcode RNA (radiolabeled at the 3′-end) was incubated overnight in cleavage buffer in the presence (lane 3) or absence (lane 4) of 10 mM manganese and then analyzed on a denaturing polyacrylamide gel alongside alkaline and ribonuclease T1 hydrolysates (lanes 1 and 2, respectively). (C) The metal dependence of self-cleavage in zipcode RNA. RNA was incubated overnight in the presence of the indicated metal. Weak cleavage with Cu²⁺ has been reported previously for the manganese ribozyme (53); whereas, Zn²⁺ triggers nonspecific degradation.