FUNCTIONAL INTERACTION BETWEEN THE ESTROGEN-RECEPTOR AND CTF1 - ANALYSIS OF THE VITELLOGENIN GENE B1 PROMOTER IN YEAST

Eukaryotic gene expression depends on a complex interplay between the transcriptional apparatus and chromatin structure. We report here a ye ast model system for investigating the functional interaction between the human estrogen receptor (hER) and CTF1, a member of the CTF/NFI tr anscription factor family, We show that a CTF1-fusion protein and the hER transactivate a synthetic promoter in yeast in a synergistic manne r. This interaction requires the proline-rich transactivation domain o f CTF1, When the natural estrogen-dependent vitellogenin B1 promoter i s tested in yeast, CTF1 and CTF1-fusion proteins are unable to activat e transcription, and no synergy is observed between hER, which activat es the B1 promoter, and these factors. Chromatin structure analysis on this promoter reveals positioned nucleosomes at -430 to -270 (+/-20 b p) and at -270 to -100 (+/-20 bp) relative to the start site of transc ription. The positions of the nucleosomes remain unchanged upon hormon e-dependent transcriptional activation of the promoter, and the move p roximal nucleosome appears to mask the CTF/NFI site located at -101 to -114. We conclude that a functional interaction of hER with the estro gen response element located upstream of a basal promoter occurs in ye ast despite the nucleosomal organization of this promoter, whereas the interaction of CTF1 with its target site is apparently precluded by a nucleosome.