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.
Department of Biological Chemistry, University of California, Irvine, California 92697-1700, USA.
M
M
Oakes
J P
JP
Aris
J S
JS
Brockenbrough
H
H
Wai
L
L
Vu
M
M
Nomura
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