Skip to content
Login Register

#RNA polymerase I

2 public questions tagged with this topic.

Processing of rRNA and tRNA

In eukaryotes, rRNA is transcribed as

Eukaryotic nucleolar rDNA tandem repeats are transcribed by RNA polymerase I as large 45S pre-rRNA, about 13 kb in humans, containing 5'ETS, 18S, ITS1, 5.8S, ITS2, 28S and 3'ETS. Non-transcribed spacers flank units. This single precursor ensures equimolar production of small and large subunit rRNAs. Co-transcriptional modification by H/ACA and C/D snoRNPs adds pseudouridines and 2'-O-methyl groups. Stepwise cleavage by endonucleases and exonucleases excises spacers, separating 18S for 40S and 5.8S-28S complex for 60S, while 5S is made by Pol III elsewhere.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6, Eukaryotic 45S pre-rRNA processing in nucleolus

View Details
Transcription in Eukaryotes

RNA polymerase I transcribes

RNA polymerase I is localized to fibrillar center of nucleolus and devoted exclusively to ribosomal RNA production, accounting for up to sixty percent of total cellular transcription in proliferating cells. It transcribes a single tandem repeat locus into large 47S precursor in mammals, 45S in mice, containing 18S, 5.8S, and 28S sequences separated by external and internal transcribed spacers. Spacer regions are removed by endo and exonucleases guided by snoRNAs. Promoter includes core element and upstream control element bound by selectivity factor SL1 and UBF architectural factor.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6: Pol I transcribes 5.8S, 18S, 28S rRNA; Lodish 9th ed., Nucleolar transcription

View Details