[1] Pol I is a 590 kDa enzyme that consists of 14 protein subunits (polypeptides), and its crystal structure in the yeast Saccharomyces cerevisiae was solved at 2.8Å resolution in 2013.
It is flanked by non-transcribed spacers NTS1 and NTS2, and is transcribed backwards by Pol III, separately from the rest of the rDNA.
Myc is known to bind to human ribosomal DNA in order to stimulate rRNA transcription by RNA polymerase I.
[8] Two specific mechanisms have been identified, ensuring proper control of rRNA synthesis and Pol I-mediated transcription.
While elongation proceeds unimpeded in vitro, it is unclear at this point whether this process happens in a cell, given the presence of nucleosomes.
In addition, UBF might also act as positive feedback, enhancing Pol I elongation through an anti-repressor function.
An additional factor, TIF-IC, can also stimulate the overall rate of transcription and suppress pausing of Pol I.
In higher eukaryotes, TTF-I binds and bends the termination site at the 3' end of the transcribed region.
In a yeast mutant strain defective in RNA polymerase I the HOT1 activity in promoting recombination is abolished.