and 2 μg proteinase K, and were incubated for additional 15 min. The samples were separated by electrophoresis on nondenaturing polyacrylamide gel in 1× TBE.

Nuclease protection assays
The reaction mixtures (25 μl) contained 25 mM HEPES–NaOH (pH 7.5), 50 mM sodium acetate, 10 mM Mg(CH3COO)2, 1 mM DTT, 0.25 mg/ml BSA, 0.5 mM ATP-γ-S, 0.5