Ultrastructural changes in the Schizosaccharomyces pombe nucleolus following the disruption of the gar2+ gene, which encodes a nucleolar protein structurally related to nucleolin.
The nucleolar protein gar2, from the fission yeast Schizosaccharomyces pombe, is the functional homolog of NSR1 from Saccharomyces cerevisiae, and is structurally related to nucleolin from vertebrates. By immunocytochemistry at the electron microscope level, we show that gar2 co-localizes with RNA polymerase I and the gar1 protein along the dense fibrillar component of the nucleolus in a wild-type strain of S. pombe, suggesting that gar2 is involved in the transcription and/or in the early steps of maturation of the ribosomal RNAs. Since the effects of disruption of the gar2+ gene might also shed light on the role of the gar2 protein, we analyzed the ultrastructure of the nucleolus of a gar2-disruption mutant. The nucleolus of the gar2- mutant is dramatically reorganized when compared with that of the wild-type gar2+ strain: a truncated protein containing the NH2-terminus of the gar2 protein is accumulated in an unusual nucleolar "dense body". Our results also suggest that the NH2-terminus might be sufficient for nucleolar localization via interaction with specific nucleolar components and support the hypothesis that gar2 in wild-type S. pombe interacts with nascent pre-rRNA via its two RNA-binding domains in combination with the glycine/arginine-rich domain. We also report that disruption of the gar2+ gene results in a mutant that is defective in cytokinesis and nuclear division.
Léger-Silvestre
I
I
Laboratoire de Biologie Moléculaire des Eucaryotes du CNRS, 118 Route de Narbonne, F-31062 Toulouse, France.
Gulli
M P
MP
Noaillac-Depeyre
J
J
Faubladier
M
M
Sicard
H
H
Caizergues-Ferrer
M
M
Gas
N
N
D002466:Cell Nucleolus / Q000648:ultrastructure*; D004275:DNA, Ribosomal / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization / Q000379:methods; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012318:RNA Polymerase I / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012335:RNA, Ribosomal / Q000235:genetics / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D020718:Ribonucleoproteins, Small Nucleolar; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000166:cytology / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins
D004275:DNA, Ribosomal; D005656:Fungal Proteins; C094395:GAR2 protein, S pombe; D009687:Nuclear Proteins; D012335:RNA, Ribosomal; D020718:Ribonucleoproteins, Small Nucleolar; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; C073180:GAR1 protein, S cerevisiae; D012318:RNA Polymerase I