Rrn7 is a subunit of the yeast Pol I core factor. It associates strongly with both Rrn6 and Rrn11 to form a complex which itself binds the TATA-binding protein, and is required for transcription by the core domain of the RNA Pol I promoter [, , ].Rrn7 human orthologue, TATA box-binding protein-associated factor RNA polymerase I subunit B (TAF1B), is also a component of RNA polymerase I core factor complex. It acts as a GTF2B/TFIIB-like factor and plays a key role in multiple steps during transcription initiation []. Both Rrn7 and TAF1B are TFIIB-like factors. Although distantly related, they share many activities associated with TFIIB-like factors [].
This entry represents subunit A (TATA-binding protein-associated factor TAFI48 or TAF1A) of RNA polymerase I. It is a component of the transcription factor SL1/TIFIB complex involved in the assembly of the pre-initiation complex (PIC). The SL1/TIFIB complex is composed of TBP (TATA-binding protein) and TAF1A (TAFI48), TAF1B (TAFI63) and TAF1C (TAFI110) []. Human ribosomal RNA synthesis by RNA polymerase I requires the activator UBF and the promoter selectivity factor SL1/TIFIB. Both TAF1B/TAFI63 and TAF1C/TAFI110 contact the promoter, whereas TAF1A/TAFI48 serves as a target for interaction with UBF and is required to form a transcriptionally active SL1/TIFIB complex responsive to UBF []. Interaction of the SL1/TIFIB subunits with TBP excluded interaction with the transcription factor IID (TFIID) subunits []. This mutually exclusive binding directs the formation of promoter- and RNA polymerase-selective TBP-TAF complexes. Therefore, TAF1A/TAFI48 may function both as a target to mediate UBF activation and as a class-specific promoter selectivity factor.
