A Translation Regulatory Particle Containing theXenopus Oocyte Y Box Protein mRNP3+4*
- From the Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan 48202
Abstract
In oocytes, nontranslated maternal mRNAs are packaged by protein into messenger ribonucleoprotein particles (mRNPs) that are masked from translation by protein-RNA interactions. Proteins associated with such masked states of mRNAs are particularly abundant in amphibian oocytes. One of these mRNP proteins fromXenopus oocytes, mRNP3+4 (also called FRG Y2a/b or p54/p56), binds to diverse mRNAs independent of their sequence and is the germ line member of the evolutionarily conserved Y box protein multigene family. Xenopus oocytes contain soluble pools of mRNP3+4 6 S oligomers, probably dimers, and larger ∼15 S particles containing mRNP3+4 and additional proteins. Here we report the purification of this larger form as an ∼320-kDa particle that contains mRNP3+4 and nine additional polypeptides, including mRNA-binding polypeptides of 34 and 36 kDa and a doublet of 110/105 kDa that proved to be nucleolin. The particle has a protein kinase activity that phosphorylates its own mRNP3+4, nucleolin, and a 31-kDa polypeptide component and exhibits translational inhibition in both the wheat germ extract and rabbit reticulocyte lysate systems. The presence of mRNP3+4 and nucleolin in this large translation regulatory particle suggests that it participates in an early step of mRNP assembly and masking.
Footnotes
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↵* This work was supported by National Science Foundation Grant MCB-9513751 and by the Michigan Research Excellence Fund.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
This work is dedicated to the memory of Dr. Robert H. Rownd, Founding Director of the Center for Molecular Medicine and Genetics.
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↵‡ To whom correspondence should be addressed: CMMG, 5047 Gullen Mall, Detroit, MI 48202. Tel.: 313-577-4346; Fax: 313-577-6200; E-mail:mmurray{at}cmb.biosci.wayne.edu.
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↵1 The abbreviations used are: mRNPs, messenger ribonucleoprotein particles; RNPs, ribonucleoprotein particles; hnRNP, heterogeneous nuclear ribonucleoprotein particle; WGE, wheat germ extract; RRL, rabbit reticulocyte lysate; GFC, gel filtration chromatography; PAGE, polyacylamide gel electrophoresis; TRP, translation regulatory particle.
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- Received September 23, 1996.
- Revision received January 29, 1997.
