text: Pol I requires no TATA box in the promoter, instead relying on an upstream control element (UCE) located between −200 and −107, and a core element located between −45 and +20.
  #The dimeric eukaryotic upstream binding factor (UBF) binds the UCE and the core element.
  #UBF recruits and binds a protein complex called SL1 in humans (or TIF-IB in mouse), composed of the TATA-binding protein (TBP) and three TBP-associated factors (TAFs).
  #The UBF dimer contains several high-mobility-group boxes (HMG-boxes) that introduce loops into the upstream region, allowing the UCE and the core elements to come into contact.
  #RRN3/TIF-IA is phosphorylated and binds Pol I.
  #Pol I binds to the UBF/SL1 complex via RRN3/TIF-IA, and transcription starts.
  Note that this process is variable in different organisms.