RNA polymerase activities in the cytoplasm of differentiating chick muscle cells

Abstract

Three distinct activities which catalyze the incorporation of radioactivity from [ 3H]UTP into acid-precipitable material have been recovered from the cytoplasm of embryonic chick muscle cells. On the basis of an analysis of their in vitro products, one of them is due to an enzyme which adds terminally to RNA; however, two others are DNA-dependent and synthesize RNA heteropolymers. One of the latter two is recovered cosedimenting with polyribosomes. These activities have properties distinct from nuclear DNA-dependent RNA polymerases described by others and from nuclear RNA polymerases found in chick embryonic muscle cells, and consequently it seems probable that they function in the cytoplasm in vivo. Since the activity found cosedimenting with polyribosomes is sensitive to α-amanitin, it is unlikely to be of mitochondrial origin.