RNA polymerases (RNAP or Pol; EC 126.96.36.199) are highly conserved multisubunit enzyme complexes (14, 12, and 17 subunits for RNAP1-3, respectively) in eukaryotes. By responding to changes in the cellular environment, transcription by RNA polymerase I ultimately determines ribosome production and the potential for cell growth and proliferation. RNAP1 is unique in that in most eukaryotes its sole function is the transcription of genes encoding the large rRNAs. Like Pol II and Pol III, it requires auxiliary factors that mediate promoter recognition, promote transcription elongation, and facilitate transcription termination.
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