Interaction of RNA polymerase with polyoma DNA

Abstract

Large amounts of purified RNA polymerase were able to attach to circular polyoma DNA I in solutions of low ionic strength. The stoichiometry of the reaction suggested that the amount of polymerase which bound was limited only by space on the DNA. Enzyme attached in this way lost most or all of its activity. At higher ionic strengths, where the enzymic activity was optimal, the maximum amount of enzyme which could bind to DNA was much smaller and saturated at 0.6 to 0.9 μg polymerase per μg polyoma DNA—indicating that the enzyme had specificity for only a few sites on polyoma DNA. In low salt solutions, where non-specific attachment readily occurred, the enzyme sedimented primarily at about 21 s. At the higher ionic strengths where only the specific binding took place, the enzyme sedimented at 13 s. Evidence is presented which suggests that the 13 s units are heterogeneous both with respect to their capacity to form 21 s particles and with respect to their capacity to bind non-specifically to the DNA. The polymerase units which formed the faster sedimenting configurations most readily also bound non-specifically to the DNA most readily.