Figure 3.

Magnesium dependence of products from internally radiolabeled precursor. Reactions were run for 1 h in HxMg buffer consisting of 50 mM Hepes (25 mM Na⁺) at pH 7.5, 135 mM KCl, and x mM MgCl₂, where x is listed below the plots and above the corresponding lanes of the gel. The gel shows a typical reaction with 1 mM pG and 30 μM d(AnTnGnAnCn)rU. Each plot is the average of two independently run assays, and the error of each point is typically ±6% of the average value. Circles represent the 5′ exon–intron product generated by either trans-splicing or intron–3′ exon junction hydrolysis. Squares represent the intron products formed either by splicing or by hydrolysis at both the 5′ exon–intron and intron–3′ exon junctions. Results are shown in the presence of 1 mM pG and 30 μM d(AnTnGnAnCn)rU (a), in the absence of added hexamer (b), in the absence of pG and in the presence of 30 μM d(AnTnGnAnCn)rU (c), and in the absence of pG and d(AnTnGnAnCn)rU (d).