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Title: Studies on nuclear RNA polymerases and the role of cyclic nucleotides on transcription
Author: Nadjat-Shokouhi, Amira
ISNI:       0000 0001 3407 1139
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1978
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1. An assay for measuring the endogenous RNA polymerase activity in Tetrahymena pyriformis nuclei was developed. The reaction rate was linear for 60 minutes at 25°C. This rate of the reaction was dependent on the presence of four nucleoside triphosphates (ATP, GTP, CTP and UTP), Mn++ or Mg++ ions, and was optimal at high concentrations of KC1 or (NHO4)2804, (0.15 M). 2. α-amanitin (a specific inhibitor of RNA polymerase II) was used to differentiate between the different classes of nuclear RNA polymer­ases, RNA polymerase I and RNA polymerase II. 3.6 x 10−4 M α-amanitin inhibited approximately 601 of total RNA polymerase activity in nuclei isolated from logarithmically growing cells. Thus about two-thirds of the nuclear RNA polyiserasa activity was due to RNA polymerase II. 3. Cyclic AMP or dibutyryl cyclic AMP stimulated nuclear RNA polymerase activity at physiological concentrations (10−6 - 10−8 M). Maximum stimulation was obtained using 10−7 M cyclic AMP or 10−7 M dibutyryl cyclic AMP. The increase .in activity stimulated by cyclic AMP in isolated nuclei was dependent on salt concentration. Cyclic AMP stimulated endogenous RNA polymerase I and inhibited endogenous RNA polymerase II activity. Chromatin-bound RNA polymarase activity was also stimulated by this cyclic nucleotide. 4. Cyclic CMP or dibutyryl cyclic GMP in the presence of CaClg stimulated nuclear RNA polymerase activity at physiological concentrations (10−88 - 10−10 M). Maximum stimulation of nuclear RNA polymerase activity by cyclic GMP in the presence of 2 mM CaCl2 occurred at 10“10 M cyclic nucleotide. 10”8 M dibutyryl cyclic GMP plus 2 mM CaCl2 produced maximum stimulation. The stimulation was CaCl2 dependent. 5 No significant stimulation of nuclear RNA polymerase activity was observed with 5'-AMP, 5'-GMP or 3',5'-cyclic CMP. 6. Chromatin-bound cyclic GMP and cyclic AMP phosphodiesterases (degrading enzymes of cyclic GMP and cyclic AMP respectively) were demonstrated to occur in Tetrahymana pyriformia nuclei. 7. The levels of total SNA polymerase activity were determined during the course of the natural cell cycle. By using α-amanitin, approximately two-thirds of the activity during the S phase of the cell cycle was found to be due to RNA polymerase II. RMA polymerase I activity was predominant in the G2 phase of the cell cycle. 8. An assay for endogenous protein kinase activity in Tetrahymena pyriformia nuclei was developed and validated. The cyclic AMP- dependent phosphorylation of nuclear proteins was found to be a salt- dependent process. Dibutyryl cyclic AMP stimulated the phosphorylation of the endogenous protein (s) and.exogenous substrates in a.partially purified nuclear fraction -containing RNA polymerase activity by 5-fold.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry