Mutational analysis of the structure and localization of the nucleolus in the yeast Saccharomyces cerevisiae.
The nucleolus in Saccharomyces cerevisiae is a crescent-shaped structure that makes extensive contact with the nuclear envelope. In different chromosomal rDNA deletion mutants that we have analyzed, the nucleolus is not organized into a crescent structure, as determined by immunofluorescence microscopy, fluorescence in situ hybridization, and electron microscopy. A strain carrying a plasmid with a single rDNA repeat transcribed by RNA polymerase I (Pol I) contained a fragmented nucleolus distributed throughout the nucleus, primarily localized at the nuclear periphery. A strain carrying a plasmid with the 35S rRNA coding region fused to the GAL7 promoter and transcribed by Pol II contained a rounded nucleolus that often lacked extensive contact with the nuclear envelope. Ultrastructurally distinct domains were observed within the round nucleolus. A similar rounded nucleolar morphology was also observed in strains carrying the Pol I plasmid in combination with mutations that affect Pol I function. In a Pol I-defective mutant strain that carried copies of the GAL7-35S rDNA fusion gene integrated into the chromosomal rDNA locus, the nucleolus exhibited a round morphology, but was more closely associated with the nuclear envelope in the form of a bulge. Thus, both the organization of the rDNA genes and the type of polymerase involved in rDNA expression strongly influence the organization and localization of the nucleolus.
Oakes
M
M
Department of Biological Chemistry, University of California, Irvine, California 92697-1700, USA.
Aris
J P
JP
Brockenbrough
J S
JS
Wai
H
H
Vu
L
L
Nomura
M
M
D002466:Cell Nucleolus / Q000235:genetics / Q000648:ultrastructure*; D015825:Chromosomes, Fungal / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics*; D008854:Microscopy, Electron; D016296:Mutagenesis; D010957:Plasmids; D012318:RNA Polymerase I / Q000378:metabolism; D012341:RNA, Ribosomal, 5S / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000648:ultrastructure*; D017384:Sequence Deletion; D014158:Transcription, Genetic
D004275:DNA, Ribosomal; D012341:RNA, Ribosomal, 5S; D012318:RNA Polymerase I