Preferential stimulation of transcription from simian virus 40 late and adeno IVa2 promoters in a HeLa cell extract.

Transcription of certain SV40 and adenovirus genes can be selectively enhanced under suitable in vitro assay conditions. The major SV40 late promoters and the adeno IVa2 promoter do not have TATA box sequences upstream from the start sites of transcription. Analyses of transcripts synthesized in vitro from the SV40 late promoters by "run-off" and S1 nuclease mapping methods show that when transcription takes place in the presence of 15 mM (NH4)2SO4, there is a 3- to 5-fold stimulation of RNA synthesis initiating from the late promoter at map position 185 and from the SV40 early promoters. RNA initiating from map position 325 is stimulated 40-fold under these conditions. When the (NH4)2SO4 concentration is increased to 50 mM (NH4)2SO4, there is a 90% suppression of transcription. Ammonium sulfate also enhances transcription from the adeno IVa2 promoter, which is not expressed in extracts that lack (NH4)2SO4 (Fire, A., Baker, C. C., Manley, J. L., Ziff, E. B., and Sharp, P. A. (1981) J. Virol. 40, 703-719; Lee, D. C., and Roeder, R. G. (1981) Mol. Cell. Biol. 1, 635-651). These modified assay conditions may allow detection of new classes of promoters.