New Inhibitors of RNA Synthesis in vitro Isolated from Escherichia coli

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Abstract
Three inhibitor proteins (I1, I2, and I3) were isolated from Escherichia coli. They depress the transcription of E. coli and T3 phage DNA by DNA‐dependent RNA polymerase from E. coli and show the following characteristics. The inhibitors I1 and I3 consist of subunits; I2, behaves as a single protein in dodecylsulfate‐polyacrylamide gel electrophoresis. Neither the initiation of the transcription of E. coli DNA nor the size of the RNA synthesized is influenced by the inhibitors. In an E. coli DNA‐dependent system reinitiation of RNA synthesis at high salt concentration seems to be blocked by the inhibitors. When inactivated, the inhibitors stimulate RNA synthesis and behave like termination factors giving rise to the production of RNA molecules of discrete size, shorter than those of control experiments. It is suggested by hybridization competition experiments that the inhibitors I1 and I3 preferentially inhibit ribosomal RNA synthesis. The inhibitors also depress the transcription of T3 phage DNA by E. coli RNA polymerase resulting in the synthesis of discrete RNA species smaller than those of control experiments without KCl as well as with 0.16 M KCl.