Pseudo-NORs: a novel model for studying nucleoli.
Nucleolar organiser regions (NORs) are comprised of tandem arrays of ribosomal gene (rDNA) repeats that are transcribed by RNA polymerase I (Pol I), ultimately resulting in formation of a nucleolus. Upstream binding factor (UBF), a DNA binding protein and component of the Pol I transcription machinery, binds extensively across the rDNA repeat in vivo. Pseudo-NORs are tandem arrays of a heterologous DNA sequence with high affinity for UBF introduced into human chromosomes. In this review we describe how analysis of pseudo-NORs has provided important insights into nucleolar formation. Pseudo-NORs mimic endogenous NORs in a number of important respects. On metaphase chromosomes both appear as secondary constrictions comprised of undercondensed chromatin. The transcriptional silence of pseudo-NORs provides a platform for studying the transcription independent recruitment of factors required for nucleolar formation by this specialised chromatin structure. During interphase, pseudo-NORs appear as distinct and novel sub-nuclear bodies. Analysis of these bodies and comparison to their endogenous counterpart has provided insights into nucleolar formation and structure.
Prieto
José-Luis
JL
Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, DD1 9SY Scotland, UK.
McStay
Brian
B
D002453:Cell Cycle / Q000502:physiology; D002466:Cell Nucleolus / Q000378:metabolism* / Q000648:ultrastructure; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D002877:Chromosomes, Human; D004275:DNA, Ribosomal / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009697:Nucleolus Organizer Region / Q000378:metabolism* / Q000648:ultrastructure; D035463:Pol1 Transcription Initiation Complex Proteins / Q000235:genetics / Q000378:metabolism; D012318:RNA Polymerase I / Q000378:metabolism; D014158:Transcription, Genetic
D002843:Chromatin; D004275:DNA, Ribosomal; D035463:Pol1 Transcription Initiation Complex Proteins; C063844:transcription factor UBF; D012318:RNA Polymerase I