Upstream Binding Transcription Factor (UBTF)

Upstream binding factor (UBF) is a transcription factor required for expression of the 18S, 5.8S, and 28S ribosomal RNAs, along with SL1 (a complex of TBP and multiple TBP-associated factors or 'TAFs'). Two UBF polypeptides, of 94 and 97 kD, exist in the human (Bell et al., 1988). UBF is a nucleolar phosphoprotein with both DNA binding and transactivation domains. Sequence-specific DNA binding to the core and upstream control elements of the human rRNA promoter is mediated through several HMG boxes.

Recognizes the ribosomal RNA gene promoter and activates transcription mediated by RNA polymerase I through cooperative interactions with the species-specific factor SL1. It binds specifically to the upstream control element.