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Heat treatment of yeast nuclear extracts abolished the capacity to initiate transcription at RNA polymerase II promoters. Activity was restored by the addition of both recombinant yeast TFIID and partially purified factor b, a yeast fraction shown previously to be required for polymerase II transcription. On the basis of this assay with heat-treated extract, factor b was purified to virtual homogeneity. The factor appears to comprise polypeptides of approximately 85, 75, and 50 kDa, since these three polypeptides co-purify with activity, and since a native mass of about 200 kDa is estimated from glycerol gradient sedimentation and gel filtration.


Journal article


The Journal of biological chemistry

Publication Date





19000 - 19005


Department of Cell Biology, Fairchild Center, Stanford University School of Medicine, California 94305.


Hela Cells, Humans, Saccharomyces cerevisiae, RNA Polymerase II, Transcription Factors, Electrophoresis, Polyacrylamide Gel, Transcription, Genetic, Kinetics, Thermodynamics