RNA Polymerase I Transcription
RNA polymerase I (Pol I) transcription occurs in the nucleolus, a non-membrane-bound nuclear organelle, where a multimeric Pol I complex transcribes from ribosomal DNA (rDNA) repeats 47S pre-ribosomal RNA, which is then being processed into 28S, 18S, and 5.8S mature ribosomal RNAs (rRNAs).
Eukaryotic RNA polymerase I complex consists of 14 subunits with a 10-subunit catalytic core that is structurally and functionally conserved among all three eukaryotic RNA polymerases. In addition to the Pol I complex itself, the Pol I machinery contains two transcriptional factors, a dimer of upstream binding factor (UBF) and multimeric complex selectivity ligand 1 (SL1/TIF-IB), an initiation factor RRN3/TIF-IA, and a termination factor TTF-I. Additional proteins, e.g., topoisomerases I and IIa, sirtuin 7, PCAF, G9a, nuclear actin and myosin (NM1), Ku70/80, PCNA, TFIIH, CSB, and many others, were...