Resolution of factors required for the initiation of transcription by yeast RNA polymerase II.

Fractionation of a yeast nuclear extract reveals at least four factors required in addition to RNA polymerase II for accurate initiation of transcription. One of these factors can be replaced by HeLa transcription factor IID or by its yeast counterpart expressed in Escherichia coli. Each of the remaining three factors can be replaced by a fraction from yeast whole cell extract, facilitating further purification of the factors.