RNA-polymerase activity in isolated nuclei of developing silkworm embryos

Nuclei isolated from developing embryos of the silkworm (Bombyx mori) are capable of RNA synthesis in vitro. The incorporation of C-14-uridine triphosphate (C-14-UTP) into the acid-insoluble fraction requires the presence of the other three ribonucleoside triphosphates; it is inhibited by actinomycin, olivomycin, and ethidium bromide, and is stimulated by ammonium sulfate. In a medium of moderate ionic strength C-14-UTP incorporation is slightly inhibited by alpha-amanitine (4 mug/ml), whereas in the presence of 0.2 M ammonium sulfate the same alpha-amanitine concentration reduces the incorporation by 90%. These data indicate that silkworm embryo nuclei, like nuclei from several other sources, contain two different RNA-polymerase fractions.