Effects of sodium selenite and selenate on DNA and RNA synthesis in vitro

The effects of sodium selenite and sodium selenate on DNA and RNA synthesis have been examined using intact HeLa cells, isolated nuclei and extracted polymerases. Selenate had no effect on any of the systems examined. Selenite inhibited DNA synthesis in intact cells and in isolated nuclei, and to a limited extent also inhibited DNA polymerase α. Selenite also inhibited RNA synthesis in intact cells and α-amanitin resistant RNA synthesis in isolated nuclei (i.e., synthesis catalyzed by RNA polymerases I and III). It had no effect on α-amanitin sensitive synthesis (catalyzed by RNA polymerase II) at concentrations up to 500 μM. However, transcription of exogenous DNA by extracted RNA polymerase II (as well as by polymerases I and III) was inhibited by selenite.