Number of engaged polymerase complexes in liver nuclei in vitro

Range 25,000-35,000 (60% of which are pol I) complexes/nucleus
Organism Rat Rattus norvegicus
Reference Jackson DA, Pombo A, Iborra F. The balance sheet for transcription: an analysis of nuclear RNA metabolism in mammalian cells. FASEB J. 2000 Feb14(2):242-54. p.244 left column top paragraphPubMed ID10657981
Primary Source [33] Coupar, B. E. H., Davies, J. A., and Chesterton, C. J. (1978) Quantification of hepatic transcribing RNA polymerase molecules, polyribonucleotide elongation rates and messenger RNA complexity in fed and fasted rats. Eur. J. Biochem. 84, 611–623PubMed ID639806
Method "Various factors complicate the analysis of nascent transcripts labeled in vivo (30, 32). However, in principle, it should be a simple matter to establish the number of nascent transcripts as cells have the same number of active pols. Numbers of active pols can be determined in vitro using purified nuclei and defined conditions with labeled precursors of known specific activity and inhibitors to establish levels of synthesis by the different pols. Following incorporation, the amounts of radiolabel at internal and terminal positions of the nascent chains allow the number of active complexes to be established."
Comments "Using this approach [see measurement method], rat liver nuclei were shown to have 25,000–35,000 engaged polymerase complexes, 60% of which were pol I (primary source). However, this type of analysis is complicated by variable recoveries of active pols in nuclei and the behavior of different enzymes under the various conditions used (33–35)."
Entered by Uri M
ID 111165