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Increased Activity of Chromatin-bound Ribonucleic Acid Polymerase from Soybean Hypocotyl with Spermidine and High Ionic Strength ¹

^a Department of Botany, University of Illinois, Urbana, Illinois 61801

Optimal activity of chromatin-bound RNA polymerase from soybeans is obtained with 1 mM Mn^2–, but only when high ionic strength or polyamines are included in the medium. Such inclusion does not increase the Mg²⁺ activation of the polymerase, but it does lower the concentration needed for optimum activity from 10 mM to 1 mM. Mg^2– activation is inhibited by added Mn²⁺, and the inhibition is relieved by high ionic strength or spermidine. The RNA polymerase with either cation is almost entirely polymerase I at low and high ionic strength as evidenced by insensitivity to -amanitin. Treatment of soybean seedlings with 2,4-dichlorophenoxyacetic acid does not change these characteristics; although the activity rises 3- to 4-fold.

It is suggested that chromatin as prepared here may be a selected fraction enriched in polymerase I, which is activated by either Mg²⁺ or Mn²⁺, and that the Mn^2– inhibition of activity is due to a known reaction of Mn^2– with DNA which can be relieved by high ionic strength.