To determine the cleavage sites, the products of the RNA fragmentation reaction along with the products of alkaline hydrolysis and limited T1 nuclease digestion of the same RNA molecule were separated on 10% polyacrylamide gels containing 7.5 M urea, 90 mM Trisborate buffer and 2 mM EDTA,. The alkaline hydrolysis ladder was generated by the incubation of the labeled RNA in formamide containing 0.5 mM MgCl 2 at 1008C for 10 min. The partial T1 ribonuclease digestion of RNAs was performed under semi-denaturing conditions (10 mM sodium citrate pH 5.0; 3.5 M urea) with 0.2 U/ml of the enzyme and incubation at 558C for 15 min. Electrophoresis was performed at 1500 V and was followed by autoradiography at À808C with an intensifying screen.