Yonghong Ren1, Rose K. Busch1, László Perlaky1, Harris Busch1
1Department of Pharmacology, Baylor College of Medicine, Houston, USA
Tóm tắt
Proteinp120 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.
