Isolation of yeast transcription factor IIA using a functional transcription assay

TFIIA was extensively purified from a whole-cell transcription extract from yeast. Activity was followed throughout isolation utilizing a functional transcription assay. Transcription activity was found to copurify with polypeptides of 43 and 12.5 kDa, consistent with a previous purification that utilized a TBP/DNA gel mobility shift assay (J. Ranish and S. Hahn, J. Biol. Chem. 266, 19320-19327, 1991). The Stoke's radius of the purified protein was determined by gel filtration chromatography to be 44 A under native conditions. The solution molecular weight derived from this measurement, 110 kDa, is consistent with a heterotetrameric structure of TFIIA.