Enzymatic Properties and Cooperative Effects in the Kinetics of Wheat‐Germ RNA Polymerases

Some of the enzymatic properties of the three classes of RNA polymerase purified from wheat germ were studied. Although the four enzyme species exhibited different template specificities using synthetic polydeoxyribonucleotides, poly(dC) was the most efficiently transcribed. Furthermore, with this matrix all enzyme forms had nearly the same specific activity (∼ 5500 units/mg). A comparative kinetic study of RNA synthesis catalyzed by the wheat germ RNA polymerases lead to the following results: when rate measurements were effected as a function of the concentration of purine nucleoside triphosphates, non-linear double-reciprocal plots were obtained for polymerases I and IIB, whereas linear plots were obtained for RNA polymerases IIA and III. The reaction rates were also measured as a function of UTP concentration (a nucleoside triphosphate which can only be used in the elongation step): the kinetics of the reactions catalyzed by RNA polymerases IIA and III can be accounted for by a simple ping-pong kinetic model; in contrast, negative cooperativity was obtained for enzymes I and IIB. This kinetic behaviour may signify that RNA polymerases I and IIB are allosterically regulated enzymes.