Recruitment of factors linking transcription and processing of pre-rRNA to NOR chromatin is UBF-dependent and occurs independent of transcription in human cells.
Efficient ribosome biogenesis requires coordination of a highly complex series of events. Early events include pre-RNA transcription, processing, and modification. Analysis in yeast has demonstrated that t-UTPs, components of the U3 snoRNA-containing pre-rRNA processing complex, are required for efficient transcription of ribosomal genes (rDNA) by RNA polymerase I (pol I). Here, we characterize human t-UTPs and establish that their ability to link transcription and pre-rRNA processing is evolutionarily conserved. The pol I transcription factor UBF binds extensively across rDNA throughout the cell cycle, resulting in a specialized form of chromatin that is the hallmark of active nucleolar organizer regions (NORs). Transcriptionally silent pseudo-NORs are ectopic, chromosomally integrated, artificial arrays that mimic this specialized chromatin structure. Pseudo-NORs sequester t-UTPs and factors linking transcription with pre-rRNA modification (Nopp140 and Treacle). Recruitment is independent of transcription, the underlying DNA sequence, and location within the nucleolus. Previously, we have demonstrated that pseudo-NORs sequester every component of the pol I transcription machinery. Taken together, these results highlight the importance of the specialized chromatin structure at active NORs in coordinating early events in ribosome biogenesis and nucleolar formation.
Prieto
José-Luis
JL
Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, DD1 9SY Scotland, United Kingdom.
McStay
Brian
B
D001483:Base Sequence; D002453:Cell Cycle; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D004275:DNA, Ribosomal / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D046912:Multiprotein Complexes; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D009697:Nucleolus Organizer Region / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D035463:Pol1 Transcription Initiation Complex Proteins / Q000378:metabolism*; D012318:RNA Polymerase I / Q000235:genetics / Q000378:metabolism; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D034741:RNA, Small Interfering / Q000235:genetics; D020718:Ribonucleoproteins, Small Nucleolar / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D002843:Chromatin; D004275:DNA, Ribosomal; D046912:Multiprotein Complexes; C075564:NOLC1 protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D035463:Pol1 Transcription Initiation Complex Proteins; D012322:RNA Precursors; D034741:RNA, Small Interfering; D020718:Ribonucleoproteins, Small Nucleolar; C105442:TCOF1 protein, human; C117377:ribonucleoprotein, U3 small nucleolar; C063844:transcription factor UBF; D012318:RNA Polymerase I
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