Table 2.
Transcription factors cited herein
| Pol II | Pol I | |
|---|---|---|
| TBP | Interacts with other Pol II initiation factors to facilitate promoter melting and transcription start site selection | Recruited to Pol I promoter during transcription initiation, and thought to be crucial for Pol I recruitment to rDNA |
| Hmo1 | Interacts with Pol II promoters, stabilizes pre-initiation complex and mediates proper start site selection | Interacts with the entire rDNA locus, has a potentially activating role in transcription initiation and elongation |
| UBF | Binds preferentially to Pol II promoters at transcription start site, may have a role in transcription initiation, promoter escape and elongation by Pol II | Binds to rDNA and can generate nucleosome-like structures at the rDNA called ribosomal enhancesomes, has critical roles in pre-initiation complex formation, promoter escape and elongation by Pol I |
| TFIIH | Essential for transcription initiation and promoter escape by Pol II, also has a role in preventing premature arrest prior to the transition to stable elongation | Important for transcription by Pol I, seems to function as an elongation factor. |
| Spt4/5 | Promotes processive elongation by Pol II by maintaining the stability of the transcription bubble, can also promote promoter proximal pausing | Localizes to rDNA, plays a positive and negative role in transcription elongation by Pol I |
| Paf1 | Influences transcription activation, initiation, elongation and termination, promotes promoter proximal pausing by Pol II | Directly promotes Pol I transcription, possibly by preventing pausing and increasing elongation rate |
| Ccr4-Not | Important for initiation and elongation, is tethered to promoters of some Pol II genes to activate or repress transcription, can rescue stalled Pol II via interaction with TFIIS | Functions downstream of mTOR signaling pathway to control Pol I transcription |
| Spt6 | Facilitates Pol II transcription through nucleosomes, can stimulate Pol II elongation independent of nucleosomes | Required for the recruitment and retention of Pol I to the rDNA promoter |