Modified in vivo subunits of DNA-dependent RNA polymerase III in mammals

Abstract

Three subunits (simultaneously phosphorylated and glycosylated) were identified as a parts of the subfractions of DNA-dependent RNA polymerase III isolated from nuclei of 3T3 mouse fibroblast culture, A431 epidermoid carcinoma cells, and mature human placenta. Subunits with molecular weights of 60 and 45 kDa and a subunit with a molecular weight of 52 kDa (which is probably one of the basal transcription factors of RNA polymerase III) were modified in the composition of the enzyme isolated from human cells. Modifications in three polypeptides with molecular weights of 49, 45, and 42 kDa were identified in the composition of subfractions of the enzyme isolated from the mouse fibroblast culture. The 45-kDa subunit is probably a component of the basal transcription factor of RNA polymerase III, since it is not identified in the mouse enzyme.