Studies on Termination of in Vitro Ribonucleic Acid Synthesis by Rho Factor

The mechanism of action of the protein rho (ρ) in DNA-dependent RNA synthesis has been examined. While ρ can interact with DNA to form a protein-DNA complex, detailed studies of this interaction suggest that this is not the mode of action of ρ. ρ appears to interact with Escherichia coli RNA polymerase at specific DNA sites leading to the formation of RNA chains of well defined length. RNA chains synthesized in the presence or absence of ρ predominantly have uridine at their 3′-hydroxyl terminus. ρ does not affect the size of RNA chains synthesized by the T7-induced RNA polymerase. ρ acts catalytically affecting many E. coli RNA polymerase molecules and is not tightly bound in a complex. The effect of ρ can be observed on RNA chains nearly three-quarters complete, further indicating that ρ alters the growth of RNA chains at specific DNA sites. After the release of RNA chains from the RNA polymerase-DNA complex, RNA polymerase remains attached to DNA in a nonactive state. The enzyme can be released from this sequestered form by increasing the ionic strength of the reaction medium.