RNA polymerase I from higher plants. Evidence for allosteric regulation and interaction with a nuclear phosphatase activity controlled NTP pool.

RNA polymerase I was isolated from parsley cells grown in suspension culture and from soybean hypocotyls. Kinetic studies of the enzyme revealed that RNA polymerase I is an allosteric regulated enzyme. The enzyme activity was influenced by nucleoside triphosphates (NTP) and divalent cations. NTP exceeding a 1:1 ratio of these two components acted as allosteric inhibitors, contrary to free divalent cations, which had promotive effects on the RNA polymerase I. Furthermore, isolated nuclei from parsley exhibited a powerful nucleoside triphosphatase (NTPase) activity. Contrary to RNA polymerase I, this enzyme was stimulated by NTP exceeding the 1:1 ratio of NTP and divalent cations. Free divalent cations had an inhibitory effect. Assuming that a causal connection of these two processes does exist, a possible role of this NTPase would be the control of NTP pools in relation to divalent cations and thus regulating RNA synthesis.