Early experiment demonstrating DNA-dependent RNA synthesis by an RNA polymerase. RNA polymerizing activity was partially purified from E. coli and analyzed for RNA synthesis, using a template DNA of sequence (AT)_n and various rNTP substrates. Reactions took place in the presence of nonradioactive (unlabeled) rNTPs and one radiolabeled rNTP, as noted on the graph. Incorporation of radioactively labeled rNTP substrates was measured.