Identification and purification of a yeast transcriptional trans-activator: The yeast homolog of the rous sarcoma virus internal enhancer binding factor

A cis-acting transcriptional activation sequence (IES2) from the Rous sarcoma virus internal enhancer was found to stimulate transcription of a heterologous gene in Saccharomyces cerevisiae. A hamster protein (termed IBF) which binds to IES2 and stimulates transcription in vitro has previously been purified and was found to have a subunit molecular mass of 40,000 (Karnitz, L., Poon, D., Weil, P. A., and Chalkley, R. (1989) Mol. Cell. Biol. 9, 1929-1939). The identification and purification of the yeast homolog of IBF (yIBF) is reported here. Purified yIBF has a subunit molecular mass of 92,000. This protein functions as a trans-activator of transcription in a heterologous HeLa transcription extract in a cis-element sequence-dependent manner in vitro.