An RNA polymerase II transcription system from rat liver. Purification of an essential component

An enzyme system capable of supporting accurate initiation of transcription by RNA polymerase II has been prepared from rat liver. Transcription depends upon at least three activities in addition to RNA polymerase II. One activity, designated alpha, has been purified 30,000-fold to near homogeneity. From all promoters tested, the synthesis of full-length runoff transcripts by RNA polymerase II depends upon alpha. alpha appears to consist of a single 35,000-dalton polypeptide and is inactivated by N-ethylmaleimide and heat. Similarities between alpha and transcription activities in fractions TFIIB (Matsui, T., Segall, J., Weil, P. A., and Roeder, R. G. (1980) J. Biol. Chem. 255, 11992-11996) and [CB] (Samuels, M., Fire, A., and Sharp, P. A. (1982) J. Biol. Chem. 257, 14419-14427) from human cells are discussed.