Ribonucleic acid synthesis by chromatin isolated from Phaseolus aureus Roxb. : The effect of endogenous ribonuclease

In-vitro transcription in tobacco chromatin

A method is described to isolate transcriptionally active Nicotiana tabacum L. cv. Xanthi chromatin from suspension-cultured cells. Enzymatic preparation of protoplasts with solubilization of the plasma membrane, Triton X-100 and homogenization resulted in chromatin free from cellular debris. Incroporation of [(3)H]uridine triphosphate into RNA increased for more than 30 min at 30° C. Transcriptional activity was maximally stimulated at 10 mM MgCl2, 200 mM (NH4)2SO4 and 150 mM KCl. The in-vitro synthesized RNA was found to contain 3.8% polyadenylated RNA. The results of digestion studies with ribonuclease, heat and detergent inactivation studies, α-amanitin and actinomycin D inhibitor effects, as well as dependency on ribonucleotide triphosphates, showed that the activity recorded in the tobacco chromatin was bona-fide enzymatic RNA transcription. There also was marked stimulation of transcriptional activity when exogenous DNA was added to the assay mixture.

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).

Chromatin-bound DNA-dependent RNA polymarase in developing pea cotyledons : II. Polymerase activity and template availability under different growth conditions

The chromatin-bound DNA-dependent RNA polymerase activity, and template availability to added homologous RNA polymerase, were determined for pea cotyledons which were allowed to develop in different environments. Both the maximum polymerase activity and the template availability were higher in cotyledons that were developing at the faster rate. The template availability was approximately constant within an environment throughout most of the development, but differed between environments. The extra DNA sythesised, that is that above the 2C level, during cytyledon development appeared to be more utilised for RNA synthesis in slowly developing cotyledons than in more rapidly developing ones.