Effect of GTP and Other Nucleoside Triphosphates on GMP Incorporation by Isolated Cortical Nuclei

Abstract

—The concentration of GTP was found to be critically important in determining the characteristics of incorporation of GMP by DNA‐dependent RNA polymerase from rat brain nuclei. The linearity of the incorporation rate was related to the log of the GTP concentration. Three hundred μM‐GTP in the presence of the other nucleoside triphosphates (1 mM) was near to the optimal conditions in terms of maximum incorporation and linearity. The concentration of ammonium sulfate was an important factor in determining the maximum GMP and UMP incorporation. The U/G incorporation ratio was less than one at low concentrations of substrate and increased with increasing substrate or ammonium sulfate concentration. α‐Amanitin strongly inhibited the reaction, indicating that RNA polymerase II is the effective enzyme.