Locating TATA Binding Protein in the RNA Polymerase I Pre-Initiation Complex

Transcription of eukaryotic DNA into RNA is carried by three main RNA polymerases (Pols I–III). Pol I synthesizes ribosomal DNA (rDNA) into ribosomal RNA (rRNA), which has been directly linked to the rate of protein synthesis, cell growth and proliferation. The efficiency of Pols’ function is controlled by general transcription factors, which enable the enzyme to interact with promoter DNA at the initiation stage. In Saccharomyces cerevisiae , Pol I transcription initiation relies on four main factors, one of which is TATA Binding Protein (TBP). TBP is an essential universal transcription factor used by all three eukaryotic Pols. As its name eludes, TBP typically binds to TATA motifs found in promoter DNA. Interestingly, unlike Pol II and III, Pol I promoters are TATA‐less. Thus, unlike the location of TBPs in other PICs, the location and function of TBP within the Pol I PIC remains unclear. Current Cryo‐EM structures of CF‐DNA‐Pol I initiation complex leaves little room for TBP to bind to its “typical” Pols II/III position. Therefore, we hypothesize that TBP must occupy a unique location, putatively more upstream, within the Pol I PIC. Combining available structural data with previous crosslinking data of CF and TBP, we modeled the interaction between the two proteins with varying distance constraints. In addition, we analyzed TBPs location on the rDNA promoter by site‐directed hydroxyl radical cleavage experiment, known as FeBABE, where DNA phosphothioate modification probes were constructed based on our predicted models. Our results from these combinational methods elucidated that TBP locates more upstream within Pol I PIC. Support or Funding Information This work was a part of SUNY Upstate Medical School’s Summer Undergraduate Research Fellowship 2019 and was supported by National Cancer Institute (NCI), National Institute for Dental and Craniofacial Research (NIDCR), and Carol Baldwin Research Foundation. FeBABE site‐directed hydroxyl radical cleavage. A and B . Sites of FeBABE incorporation into rDNA promoter in clusters of 5 include the “typical” location of TBP (1), upstream of the CE (2), 5′ of CE (3), and within the CE (4). C . Western blot showed FeBABE specific cleavage products. Cleavages were observed when FeBABE was incorporated at all four positions. Most intense cleavages were observed when FeBABE is incorporated upstream of the CE. D . Quantitation of TBP cleavages. Figure 1