The solubilization and partial characterization of pea RNA polymerases

Purification and subunit structure of RNA polymerase II from the pea

DNA-dependent RNA polymerase II (EC 2.7.7.6) from pea seedlings (Pisum sativum var. Alaska) has been purified to homogeneity, as judged by native polyacrylamide electrophoresis. The procedure includes polyethyleneimine precipitation and elution, ammonium sulfate precipitation, DEAE-Sephadex chromatography, phosphocellulose chromatography, and heparin-Sepharose chromatography. The enzyme purified almost to homogeneity has a specific activity of 200 nmol/mg per 15 min at 30 degrees C with denatured calf thymus DNA as template. The enzyme activity is 50% inhibited in the presence of 0.05 migrograms/ml of alpha-amanitin. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate indicates that pea RNA polymerase II is composed of eight subunits with molecular weights and molar ratios (in parentheses) of 170 000 (0.9), 140 000 (1.0), 43 000 (1.5), 26 000 (2.0), 22 500 (1.2), 21 500 (0.6), 18 500 (1.6) and 17 500 (2.3). The structure is closely similar to that of cauliflower RNA polymerase II.

Large-scale purification and subunit structure of DNA-dependent RNA polymerase II from cauliflower inflorescence

DNA-dependent RNA polymerase II (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) from cauliflower inflorescence (Brassica oleracae, var. botrytis) was highly purified by polyethyleneimine treatment on a large scale. The solubilized enzyme was partially purified by polyethyleneimine fractionation and subjected to chromatography on DEAE-Sephadex and phosphocellulose, and subsequently to sedimentation in a glycerol gradient. The specific activity (231 nmol/mg per 10 min) of this enzyme was comparable to that reported for other purified eukaryotic RNA polymerases. Analysis of the purified RNA polymerase II by polyacrylamide gel electrophoresis under nondenaturing conditions revealed a single band. The subunit composition of the enzyme was analyzed by electrophoresis under denaturing conditions. The RNA polymerase II contained subunits with molecular weights and molar ratios (in parentheses) of 180 000(1), 130 000(2), 48 000(2), 25 000(4), and 19 500(4).

Template activity of synthetic deoxyribonucleotide polymers in the eukaryotic DNA-dependent RNA polymerase reaction

Template specificities of the eukaryotic DNA-dependent RNA polymerases A and B from rat liver, pea, and cauliflower have been investigated using synthetic polydeoxyribonucleotides. Polymerases A and B from the three species exhibit different specificities for single-stranded homopolymers: polymerase A preferentially reads poly(dT) and poly (dC). and polymerase B poly (dC). This preferential reading appears to be a property of eukaryotic DNA-dependent RNA polymerases. Polymerases A and B transcribe synthetic polyribonucleotides also, but at a reduced rate. The polyribonucleotides which can be read by DNA-dependent RNA polymerases have a base sequence similar to that of the polydeoxyribonucleotides, which are effeciently transcribed, suggesting that the base sequence of the template rather than its conformation is crucial in the template specificity for synthetic polymers. Competition experiments with polydeoxyribonucleotides indicate that the enzymes have different binding specificities, which are not the same as their template specificities.

Chromatin-bound DNA-dependent RNA polymerase in developing pea cotyledons

The pattern of cotyledon development in three varieties of Pisum sativum has been defined in terms of cell number, DNA and RNA content and chromatin, bound RNA polymerase activity. Variation was observed in the relative periods of growth by cell division and cell expansion between the three varieties. The mean DNA content per cotyledon cell during growth by cell expansion increased to approximately 50C in one variety, 30C in the second variety and 15C in the third variety. The pattern of chromatin-bound RNA polymerase activity during development suggested that some of the DNA above the 2C level may contribute to RNA synthesis in two of the three varieties studied. In the third variety the RNA polymerase activity decreases throughout the phase of increase in DNA per cell. The chromatin-bound RNA polymerase activity per cell was correlated with the rate of RNA increase per cell.

Isolation and purification of RNA polymerases from rye embryos

A procedure has been developed for the purification of soluble DNA-dependent RNA polymerase (EC 2.7.7.6) from rye embryos. The enzyme solubilized by high salt extraction with sonication and resolved by DEAE-cellulose chromatography yields two activities. Enzyme I eluted at 0.15 M (NN4)2SO4, was insensitive to alpha-amanitin and was extremely labile. Enzyme II eluted at 0.25 M (NH4)2SO4 was inhibited by alpha-amanitin. However, DEAE-Sephadex chromatography yields three DNA-dependent RNA polymerases. Enzyme I is resistant to amanitin, while II and III enzymes are inhibited by this poison. Partially purified on DEAE-cellulose, polymerase II was further purified by hydrophobic chromatography on an omega-aminobutyl-Sepharose column. After omega-aminobutyl-Sepharose chromatography, enzyme II was stable and was more active with denatured than with native DNA as template. The activity of purified RNA polymerase II is dependent on the DNA, Mn-2+ and Mg-2+ added and requires ATP, GTP, CTP and UTP for its maximum activity. Transcription is inhibited besides by alpha-amanitin, by chromomycin A3, daunomycin, ethidium bromide and actinomycin D. Rifampin and rifamycin SV do not inhibit the enzyme. Synthetic copolymers were also effective as templates.