Chapter 3 - rDNA gene structure, transcription, and its coregulation

Abstract

Ribosome production requires hundreds of assembly factors, many ribosomal proteins, and a few ribosomal RNAs through the coordinated activity of three RNA polymerases in eukaryotes. RNA polymerase I synthesizes the large ribosomal RNA (rRNA). The genes for large ribosomal RNAs are found in huge clusters of tandem repeats and their transcription in the nucleolus is orchestrated by the synergistic action of RNA Pol I, the upstream binding factor, and the promoter selectivity factor SL1. The 47S precursor rRNAs in human cells are processed into mature 28S, 18S, and 5.8S rRNAs before their assembly with the 5S rRNA into the mature ribosomes. Coincident with transcription, rRNAs undergo multiple modifications such as pseudouridylation and 2′-O-ribose methylation to fine-tune their structures and functions. The ribosomal protein genes are present throughout the genome and are transcribed by RNA Pol II. The 5S rRNA is transcribed by RNA pol III from multiple gene copies in the genome and the recruitment of TFIIIC to 5S rRNA promoter requires the presence of the transcription factor TFIIIA.