THE GLUCOCORTICOID RECEPTOR FUNCTIONS AT MULTIPLE STEPS DURING TRANSCRIPTION INITIATION BY RNA-POLYMERASE-II

We have used a panel of monoclonal antibodies and a cell-free transcri ption assay to study the function of the tau(1) transactivation domain of the human glucocorticoid receptor. Three antibodies (monoclonal an tibodies 250, 275, and 286) specifically inhibited tau(1)-dependent tr anscription, but had little or no effect on either basal transcription or the activity of an unrelated yeast transcription factor. This inhi bition was not due to interference of DNA binding activity, as all thr ee antibodies super shifted tau(1)-containing protein-DNA complexes. E pitopes for all three antibodies were localized to a region between am ino acids 190 and 200, which lies within the recently defined 41-amino acid core region of tau(1) that is required for transactivation (Dahl man-Wright, K., Almlof, T., McEwan, I.J., Gustafsson, J-A., and Wright , A. P. H. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 1619-1623). In c ontrast to the effect on tau(1)-dependent transcription none of the an tibodies tested antagonized the squelching ability of the tau(1) domai n, suggesting that tau(1)-mediated transactivation involves interactio ns in addition to those identified by the squelching assay. Consistent with this, a comparison of the kinetics of tau(1) squelching and inhi bition of transactivation by monoclonal antibodies suggested a role fo r tau(1) mediated transcriptional induction at two or more steps durin g transcription initiation by RNA polymerase II.