Figure 4.

(A) Time course of cleavage for truncated dtr31. Reactions were carried out in the presence of 50 mM sodium cacodylate buffer at pH 5.0 (lanes 1–6) or pH 7.4 (lanes 7–17) for the times indicated, and the samples were separated on a 20% polyacrylamide/8 M urea gel. (B) The fraction of the RNA remaining uncut was plotted against time using data from an experiment similar to A. The fraction of molecules remaining at each time point was calculated and the background at zero time was subtracted from each value. Solid and open symbols indicate the reactions at pH 5.0 and pH 7.4, respectively. (C) The rate of cleavage reaction was plotted as a function of RNA concentration. (D) Thin-layer chromatography of nuclease P-digested 5′ reaction product of dtr31 on polyethyleneimine–cellulose plates to determine the ends of cleavage. The positions of nonradioactive markers are indicated alongside.