Characterization of the RNA synthesizing activity of isolated kidney nuclei

The limiting factor in RNA synthesis by isolated kidney nuclei is RNA nucleotidyltransferase at high salt concentrations but at low salt concentrations template availability becomes limiting. alpha-Amanitin inhibits 85% of the activity at high salt concentrations but only 20-50% of the activity at low salt concentrations. Exogenous DNA is utilized at low salt concentrations [up to 0-1M (NH4)2SO4] but not at high salt concentrations. The effect of increasing salt concentration is mainly to cause an increase in the length of chains synthesized. Initiation rates are not increased by high salt concentrations. The apparent Km for UTP is 8-10 muM at high salt concentrations, indicating that assays performed at low UTP concentrations are likely to give inaccurate results. The activation energy for the reaction at low salt concentration is less than that for the reaction at high salt concentration. The RNA synthesizing capacity of kidney nuclei is dependent on the method of isolation, and preparation by a modification of the Chauveau method (Chauveau et al. 1956) yields the most active nuclei.