Transcription initiated by RNA polymerase II and transcription factors from liver: Structure and action of transcription factors ∈ and τ

We have fractionated rat liver and identified a set of transcription factors that are essential for accurate initiation by RNA polymerase II. These factors were resolved into five distinct enzyme fractions designated α, βγ, δ, ∈, and τ. Four of these fractions can now be replaced with purified proteins. α and βγ were previously purified to apparent homogeneity (Conaway, J. W., and Conaway, R. C. (1989) J. Biol. Chem. 264, 2357-2362). Here, we report purification to near homogeneity of transcription factor ∈. ∈ has a native molecular mass of approximately 90 kDa and is composed of 34- and 58-kDa polypeptides. Both the 34- and 58-kDa polypeptides are required for runoff transcription. In addition, we show that transcription factor τ is a rat liver homologue of the TATA factor (TFIID or BTF1) that can be efficiently replaced in transcription in vitro by recombinant yeast TFIID. Comparison of the two factors reveals, however, that they differ significantly in their abilities to direct the transcription system to discriminate between promoters of different sequences.