The 58-kDa microspherule protein (MSP58), a nucleolar protein, interacts with nucleolar protein p120.
Protein p120 is a proliferation-related nucleolar protein which is detectable early in the G1 phase of the cell cycle and peaks early in the S phase. Most human malignant tumors contain much higher levels of protein p120 than normal resting cells. To identify p120-associated protein(s), a yeast two-hybrid screen was carried out using protein p120 as the bait. Two positive clones encoded portions of a novel protein, designated microspherule protein 58 kDa (MSP58). MSP58 mRNA is 1.9 kb and encodes an approximately 58-kDa polypeptide of 462 amino acids as shown by Western blotting of HeLa nucleolar proteins. The mouse MSP58 homolog has 97% amino acid similarity to human MSP58, but no MSP58 homolog was found in the yeast genome. The MSP58 N-terminal region contains serine-rich clusters and its C-terminal region has a coiled-coil domain. In insect Sf9 cells, recombinant p120 and MSP58 proteins associated with each other, confirming the results of the yeast two-hybrid assay. Deletion mutations revealed that the binding of MSP58 to p120 required a previously unrecognized coiled-coil domain within the N-terminal region of p120 and the C-terminal region of MSP58 protein. Immunofluorescence indicated that the MSP58 protein is localized in microspherules in the nucleolus. Anti-MSP58 Ig labeled nucleolar 'caps' when HeLa cells were treated with actinomycin D. When the MSP58 protein was overexpressed in COS-7 cells, the nucleolus became irregularly enlarged, which suggests that MSP58 may affect the size and shape of the nucleolus.
Ren
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Department of Pharmacology, Baylor College of Medicine, Houston, TX 77030, USA.
Busch
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Perlaky
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D000595:Amino Acid Sequence; D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism; D001665:Binding Sites; D002458:Cell Fractionation; D002460:Cell Line; D002466:Cell Nucleolus / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure; D002868:Chromosomal Proteins, Non-Histone / Q000302:isolation & purification / Q000378:metabolism; D003001:Cloning, Molecular; D003433:Crosses, Genetic; D003609:Dactinomycin / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009687:Nuclear Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D011496:Protein Methyltransferases; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000502:physiology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D018411:Spodoptera; D014162:Transfection; D012359:tRNA Methyltransferases
D000951:Antigens, Neoplasm; D002868:Chromosomal Proteins, Non-Histone; C113292:MCRS1 protein, human; C485136:Mcrs1 protein, mouse; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; C047458:fibrillarin; D003609:Dactinomycin; C065028:NOP2 protein, human; C512901:Nop2 protein, mouse; D011496:Protein Methyltransferases; D012359:tRNA Methyltransferases