Association of the nucleolar transcription factor UBF with the transcriptionally inactive rRNA genes of pronuclei and early Xenopus embryos.
When nuclei (pronuclei) were assembled from sperm chromatin in Xenopus egg extract and examined by immunofluorescence microscopy, UBF was concentrated at a single intranuclear dot-like or more extended necklace-like structure. These UBF-foci contained rDNA as demonstrated by in situ hybridization and hence represent the chromosomal nucleolus organizing regions (NORs). Besides UBF, other components of the transcription machinery such as the TATA-box binding protein (TBP) and RNA polymerase I (pol I) as well as several nucleolar proteins could not be detected at the NORs. Immuno-depletion experiments indicated the UBF is maternally provided and taken up by the pronuclei. Essentially the same results were obtained when we examined the NORs of early Xenopus embryos up to the midblastula stage. After this stage, when transcription of the rRNA genes has begun, nucleoli developed and the NORs acquired TBP and pol I. Our results support the hypothesis that UBF is an architectural element which converts the rDNA chromatin into a transcriptionally competent form.
Bell
P
P
Department of Cell and Developmental Biology, Theodor-Boveri-Institute, University of Würzburg, Germany.
Mais
C
C
McStay
B
B
Scheer
U
U
D000818:Animals; D000918:Antibody Specificity; D001755:Blastocyst / Q000737:chemistry; D002467:Cell Nucleus / Q000737:chemistry / Q000235:genetics; D002843:Chromatin / Q000737:chemistry; D004275:DNA, Ribosomal / Q000032:analysis / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D005260:Female; D005455:Fluorescent Antibody Technique; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D008297:Male; D009697:Nucleolus Organizer Region / Q000235:genetics* / Q000378:metabolism; D035463:Pol1 Transcription Initiation Complex Proteins; D012318:RNA Polymerase I / Q000032:analysis / Q000276:immunology; D013094:Spermatozoa / Q000737:chemistry; D035181:TATA-Box Binding Protein; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D014982:Xenopus laevis; D012407:rRNA Operon / Q000502:physiology*
D002843:Chromatin; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D035181:TATA-Box Binding Protein; D014157:Transcription Factors; C063844:transcription factor UBF; D012318:RNA Polymerase I