Effect of the ionic environment on the transcriptional activity of rat liver nucleoli

RNA synthesis and number of transcribing polymerase molecules in ischemic liver nuclei

Nuclei isolated from ischemic liver show a consistent reduction of their RNA synthesis. The reduction persists at high ionic strength and in the presence of heparin, when RNA synthesis in vitro is fully activated and occurs in the presence as well as in the absence of alpha-amanitin. Both the number of transcribing polymerase molecules and the rate of elongation of initiated polynucleotide chains seem to be equally affected.

RNA synthesis by nuclei and nucleoli from ischemic liver cells

Nuclei and nucleoli were isolated from rat livers subjected to an interruption of the blood supply for periods of different duration, as well as after restoration of the blood supply. They were assayed for RNA synthesis under conditions of diverse ionic strengths, and in the presence of an exogenous template, such as poly d (A-T), and actinomycin to inactivate the endogenous template; alpha-amanitin was made used of to distinguish polymerase I and polymerase II dependent RNA synthesis. Nuclei and nucleoli from ischemic livers showed a severe impairment of RNA synthesis, which is likely to be due to decreased initiation frequency of the engaged polymerases, while free polymerases were essentially unchanged. Both form I and II polymerase were equally involved. After restoration of the blood supply RNA synthesis recovered with an overshooting well above normal levels of activity, lasting for at least 24 hours. Increased RNA synthesis was not followed by thymidine incorporation into DNA.