Control of ribosomal RNA synthesis in Escherichia coli. V. Stimulation of rrnC gene transcription in vitro by a protein factor.

Ribosomal RNA synthesis has been investigated in an in vitro system consisting of purified E. coli RNA polymerase and phi 80d3 DNA carrying rrnC operon. rRNA comprises about 25% of the total RNA synthesized in this system under optimal conditions and is stimulated by a crude protein fraction prepared from E. coli cell extracts. The stimulation activity has been fractionated by a Sephacryl S200 column and detected as a single peak of about 50,000 daltons molecular weight. The activity specifically increases the initiation frequency of transcription of the rRNA operon on the phage DNA. The addition of ppGpp partially inhibits the stimulation activity for rRNA synthesis.