RNA Polymerase III Promoters

RNA polymerase III transcribes small rRNA, tRNAs, and some snRNAs (see Table 13.3) and recognizes several distinct types of promoters. The promoters of snRNA genes transcribed by RNA polymerase III contain several consensus sequences that are also found in some promoters transcribed by RNA polymerase II (IFigure 13.21a). These consensus sequences include the TATA box, which is recognized by a transcription factor that contains TBP. As in other types of eukaryotic promoters, TBP positions the active site of RNA polymerase over the start site for transcription in these promoters.

Promoters for small rRNA and tRNA genes, also transcribed by RNA polymerase III, contain internal promoters that are downstream of the start site and are actually transcribed into the RNA (IFigure 13.21 b and c). These promoters contain critical sets of nucleotides (boxes A, B, and C) that also are recognized by transcription factors. One of these transcription factors includes TBP, which, again, positions the active site of RNA polymerase III over the upstream start site and ensures that the enzyme initiates transcription at the correct location. Additional transcription factors then bind to the DNA-binding factor and recruit RNA polymerase to the initiation complex. _

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