Transcription of the TATA box binding protein (TBP) gene in Acanthamoeba castellanii is regulated by TATA box binding protein promoter binding factor (TPBF), which binds to an upstream TBP promoter element to stimulate transcription, and to a TATA proximal element, where it represses transcription. In order to extend these observations to the in vivo chromatin context, the TBP gene was examined by in situ footprinting and chromatin immunoprecipitation (ChIP). Acanthamoeba DNA is nucleosomal with a repeat of approximately 160 bp, and an intranucleosomal DNA periodicity of 10.5 bp. The TBP gene comprises a 220 bp micrococcal nuclease hypersensitive site corresponding to the promoter regulatory elements previously identified, flanked by protected regions of a size consistent with the presence of nucleosomes. ChIP data indicated that TPBF is associated with the TBP, TPBF and MIL gene promoters, but not to the CSP21, MIIHC, 5SrRNA or 39SrRNA promoters, or to the MIL gene C-terminal region. Binding by TPBF to the TPBF and MIL gene promoters was confirmed by in vitro assays. These results validate the in vitro model for TBP gene regulation and further suggest that TPBF may be autoregulated and may participate in the regulation of the MIL gene.
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