TRF1 (TBP-related factor 1) shows significant similarity to TBP with approximately 63% sequence identity in the carboxy-terminal core domain (D'Alessio et al. 2009; Akhtar et al. 2011; Müller et al. 2010). Consistent with this, TRF1 interacts with TFIIA, TFIIB, and the TATA box, and mediates basal transcription by RNAPII in vitro. Furthermore, it can also direct transcription from the TC box-containing "upstream" promoter of the tudor gene in vivo. Remarkably, transcription from the TATA-containing "downstream" promoter of this gene is not directed by TRF1 but instead by TBP/TFIID. These observations indicate that TRF1 could function as a core promoter selectivity factor in living cells.
TRF1 was originally identified in Drosophila and currently appears to be specific to insects. Importantly, TRF1 forms a complex with BRF1 and mediates transcription by RNAPIII in vitro as well as in vivo. This is in stark contrast to other species