A protein required for the initiation of DNA synthesis by RNA polymerase

RNA polymerase of Shigella sonnei rif purified through DEAE-Sephadex A-50 could not initiate the synthesis of DNA using phage fd DNA as a template. A protein which could complement the polymerase to initiate the synthesis of DNA was recovered from the DEAE-Sephadex A-50 column separately from the RNA polymerase. There is apparently a protein which is required to synthesize a primer RNA for the synthesis of DNA other than the components of RNA polymerase holoenzyme of Shigella sonnei rif. The protein seems to be specifically required for the initiation of DNA synthesis and to have little effect on the synthesis of RNA.