Molecular mechanism for general regulation on transcription

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We previously identified a novel TBP-interacting protein (TIP 120 from rat liver. In this study, we demonstrated that recombinant TIP 120 activated the basal level of transcription from various kinds of promoters regardless of the template DNA topology and the presence of TFIIE/TFIIH and TAFs. Kinetic studies suggested that TIP 120 functioned during preinitiation complex formation at the step of RNAP II/TFIIF recruitment to the promoter, but not after the completion of preinitiation complex (PIG) formation. EMSA showed that TIP 120 enhanced PIG formation by overcoming a kinetic impediment to RNAP II/TFIIF integration into the TBP/TFIIB- DNA-complex. Deletion analysis demonstrated that the N-terminal 412 residues including an acidic region and the TBP-binding domain is required for TIP120 function. Interestingly, TIP 120 also stimulated RNAP I- and Ill-driven transcription in vitro. In mouse cells, ectopically expressed TIP 120 enhanced transcription from all three classes (class I, II, and III) of promoters. The TIP 120 nuclear staining patterns changed from sharp foci to large speckles upon retinoic acid treatment. Moreover, some TIP 120 regions in HEp-2 cells were colocalized with the PML oncogenic domains.