RNA Polymerase I Promoters

RNA polymerase I promoters have two functional sequences near the start site (IFigure 13.20). A core element surrounds the start site, extending from —45 to +20, and is needed to initiate transcription. An upstream control element extends from — 180 to — 107 and increases the efficiency of the core element. The DNA sequences of the core element and the upstream control element are rich in guanine and cytosine nucleotides and are similar in sequence.

RNA polymerase I requires two proteins to initiate transcription: SL1 and UBF. SL1 is made up of four sub-units, one of which is TBP—the same protein that binds the TATA box in RNA polymerase II promoters (see Figure 13.17). The other protein, UBF, binds to both the core element and the upstream control element (see Figure 13.20) and enables SL1 to bind to the promoter. SL1 then recruits RNA polymerase I to the promoter. Thus; RNA polymerase I promoters function much as RNA polymerase II promoters do: transcription factors bind to a consensus sequence in the promoter and recruit RNA polymerase to the start site.

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