Reactivation of nuclear RNA polymerase activity in growth stimulated epithelial cells

Abstract

The activation of endogenous RNA polymerases has been studied in mouse kidney epithelial cells which have been induced to grow in culture. Slide cultures were assayed for RNA polymerase, in situ, after brief fixation. Enzyme activity was detected by autoradiography. Polymerases I (nucleolar) and II (nucleoplasmic) were distinguished by localization and by the activities in the presence of different ions as well as sensitivity to α-amanitin. Kidney epithelial cells resuming their growth activity when inoculated in vitro show an early and rapid increase in nuclear size (nuclear protein content) which precedes cell multiplication. Both nucleolar and nucleoplasmic polymerase activities appear at an early phase of growth activation and increase during the whole period of growth activation in proportion to increase in nuclear size. RNA polymerases may also be activated in cells which have not undergone an increase in nuclear size if assayed in the presence of a high salt concentration (0.4 M ammonium sulphate). The role of modification of chromatin structure for genetic reactivation is discussed.