Determinants of vitellogenin B1 promoter architecture - HNF3 and estrogen responsive transcription within chromatin

The liver-specific vitellogenin B1 promoter is efficiently activated by est rogen within a nucleosomal environment after microinjection into Xenopus la evis oocytes, consistent with the hypothesis that significant nucleosome re modeling over this promoter is not a prerequisite for the activation by the estrogen receptor (ER alpha). This observation lead us to investigate dete rminants other than ER alpha of chromatin structure and transcriptional act ivation of the vitellogenin B1 promoter in this system and in vitro. We fin d that the liver-enriched transcription factor HNF3 has an important organi zational role for chromatin structure as demonstrated by DNase I-hypersensi tive site mapping. Both HNF3 and the estrogen receptor activate transcripti on synergistically and are able to interact with chromatin reconstituted in vitro with three positioned nucleosomes. We propose that HNF3 is the cellu lar determinant which establishes a promoter environment favorable to a rap id transcriptional activation by the estrogen receptor.