In vitro activation of td group I aptazymes by theophylline. a) Autoradiogram showing the splicing activity of the parental, B11, Th1P6, Th2P6 and Th1P5 intron constructs in the presence and absence of 1.5 mM theophylline. LI, linear intron; CI, circular intron; E1–E2, exon 1–exon 2 ligation product; Crp, cryptic ligation product; pre-mRNA, unspliced mRNA. b) Kinetics of splicing for Th1P5. c) Kinetics of splicing for Th2P6. For both figures, solid circles represent the reaction in the presence of 1.5 mM theophylline and open circles represent the reaction in the absence of theophylline. Data points are the average of four determinations.