The hyperthermophile archaeon, Pyrococcus furiosus encodes two eukaryotic TFIIB family proteins, TFB1 and TFB2. TFB1 is very similar to TFIIB in terms of sequence homology and function, whereas TFB2 is unusual as it is missing highly conserved sequences in its N-terminal domain that are present in TFIIB and TFB1. Despite this, TFB2 is effective in transcription process, albeit with lower efficiency compared to TFB1. Other archaea also contain multiple TFBs, but unlike Pyrococcus furiosus TFB2, these multiple TFBs have higher sequence homology to each other and have similar transcription efficiencies. Photochemical cross-linking experiments have shown that the B-reader of TFB in archaea and TFIIB in eukaryotes is close to transcription start site and is very important in RNAP recruitment to promoter DNA and transcription start site selection. Thus the lack of the highly conserved B reader region in P. furiosus TFB2 presents the opportunity to further study the functional importance of this region.
In this study several amino acids in N-terminal domain of TFB2 were mutated with photoactivable unnatural amino acid p-benzoyl L- phenylalanine (pBpa) and the proximity of TFB2 relative to DNA was determined by photochemical cross-linking experiments. The results showed that TFB2 interacts with DNA near the TATA box via its C-terminal domain, and interacts with both strands of DNA near the transcription start site via its divergent B-reader and the B-linker sequences. The B-reader loop region is close to transcription start site and interacts with the transcribed strand of promoter DNA while the B-linker strand cross-links with the non-transcribed strand. Some of the amino acids in between the B-reader loop and the B-linker strand region in TFB2 are seen to cross-link both the transcribed and the non-transcribed strand. Thus, despite the absence of strong homology to conserved B-reader and B-linker sequences, TFB2 is likely to interact with DNA in the transcription bubble and facilitate in transcription initiation.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-2938 |
| Date | 23 July 2014 |
| Creators | Bhattarai, Arati |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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