Characterization of ribonucleic acid synthesis by nuclei isolated from Zea mays

Nuclei were isolated from the shoots of Zea mays and assayed for endogenous RNA polymerase activity in vitro. Maximum incorporation from radioactive precursors (70 pmol [(3)H]uridine 5' monophosphate/100 μg DNA) was reached after incubation for 1 h at 25°C. The RNA product, analysed by polyacrylamide gel electrophoresis, was polydisperse in size with an upper limit of 2x10(6) daltons. Discrete peaks of rRNA were not detected, probably because of endogenous ribonuclease activity. The inclusion of α-amanitin (4 μg/ml) in the incubation reduced the total incorporation by approximately 40% but did not significantly alter the size of the RNA product. Although 40% of the total activity could be attributed to RNA polymerase II, [(3)H]RNA synthesised in vitro was found not to contain long sequences of poly (A).