Figure 3.

In vitro repression of transcription by CRP and Lac repressor. (A) In vitro single-round transcription reactions were performed using the proP substrate pRJ4069 in the presence (+) or absence (−) of CRP–cAMP and in the presence of 0.1–0.6 m K⁺ glutamate as denoted. The portions of the gel containing the P1 transcript and the vector rrn1 transcript are shown. The bar graph depicts the levels of the proP P1 transcript synthesized in the presence versus the absence of CRP–cAMP at each K⁺ glutamate concentration from the data shown above. (B) A similar set of reactions were performed using the substrate pKK223-3 containing the tac promoter in the presence (+) or absence (−) of Lac repressor.