Partial purification of plant transcription factors. I. Initiation.

Crude plant cell protein extracts prepared from wheat germ are inactive for in vitro transcription by RNA polymerase II. These extracts do, however, have correct initiation of transcription by RNA polymerase II. Initiation is monitored by measuring the formation of transcription complexes in vitro. A nuclear extract produces more initiation events than a whole cell extract or a cytosol extract. Some factors necessary for initiation can be separated from other proteins, including inhibitors, by ion exchange column chromatography. One specific fraction is sufficient for the formation of transcription complexes and several other fractions may be stimulatory or accessory factors.