Fig. 3. Pure calf thymus SII and a divalent metal activate RNA cleavage.

Washed elongation complexes were incubated with 36 ng of pure calf thymus SII (+) or buffer (−). Reactions were adjusted to 7 mM in MgCl₂, MnCl₂, or CaCl₂ as indicated and incubated at 28 °C for 30 min. RNA was isolated and separated on a 5% polyacrylamide gel as described under “Materials and Methods.” Migration positions of RNAs are indicated as described for Fig. 1.