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

Abstract

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 Mg(2+) 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 Mn(2+), 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 alpha-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 Mg(2+) or Mn(2+), 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.