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Proc Natl Acad Sci U S A. 2003 Jan 21;100(2):550-5. Epub 2003 Jan 13.

RFPL4 interacts with oocyte proteins of the ubiquitin-proteasome degradation pathway.

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  • 1Department of Pathology, Baylor College of Medicine, Houston, TX 77030, USA.


Oocyte meiosis and early mitotic divisions in developing embryos rely on the timely production of cell cycle regulators and their clearance via proteasomal degradation. Ret Finger Protein-Like 4 (Rfpl4), encoding a RING finger-like protein with a B30.2 domain, was discovered during an in silico search for germ cell-specific genes. To study the expression and functions of RFPL4 protein, we performed immunolocalizations and used yeast two-hybrid and other protein-protein interaction assays. Immunohistochemistry and immunofluorescence showed that RFPL4 accumulates in all growing oocytes and quickly disappears during early embryonic cleavage. We used a yeast two-hybrid model to demonstrate that RFPL4 interacts with the E2 ubiquitin-conjugating enzyme HR6A, proteasome subunit beta type 1, ubiquitin B, as well as a degradation target protein, cyclin B1. Coimmunoprecipitation analyses of in vitro translated proteins and extracts of transiently cotransfected Chinese hamster ovary (CHO)-K1 cells confirmed these findings. We conclude that, like many RING-finger containing proteins, RFPL4 is an E3 ubiquitin ligase. The specificity of its expression and these interactions suggest that RFPL4 targets cyclin B1 for proteasomal degradation, a key aspect of oocyte cell cycle control during meiosis and the crucial oocyte-to-embryo transition to mitosis.

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