Transcription, the first step in gene expression, is a highly regulated process which relies on a multi-protein complex to occur. Among these proteins are transcription factors, including initiation and elongation factors, which play differing roles in early and late stages of transcription. The mechanisms of transition from transcription initiation to elongation are not well understood in archaea, nor are the structures of the transcription factors involved. For transcription to occur in vitro, transcription factors TATA binding protein (TBP) and Transcription Factor B (TFB) are sufficient to allow RNA polymerase (RNAP) to synthesize RNA from template DNA. Another factor, Transcription Factor E (TFE), can also join the initiation complex and is likely to be essential in vivo. TFE is known to contribute to initiation by enhancing promoter opening, and while it has been shown to persist in elongation complexes, its role after initiation is unknown. Spt4/5, the archaeal homolog of the only universally conserved RNAP-associated factor, is known to join complexes in elongation steps and enhance processivity of the polymerase. However, if Spt4/5 joins pre-initiated complexes, it has been shown to inhibit transcription activity. The experiments in this thesis show that TFE and Spt4/5 participate in a crucial interchange at the upstream fork of the transcription bubble that helps define the timing of Spt4/5 binding. Using unnatural amino acid crosslinking techniques, the points of proximity between specific regions of these two factors and the template DNA have been mapped to identify possible sites of interaction. Competitive crosslinking assays indicate the exact timing of the shift in affinity between TFE and Spt4/5 for their shared binding site on RNAP. These data, combined with transcription assays, suggest a new role for TFE in preventing premature Spt4/5 binding, corresponding with a unique localized mobility within the winged helix of TFE.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-5515 |
| Date | 30 May 2018 |
| Creators | Sheffield, Kimberly Kay |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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