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Biochem Biophys Res Commun. 2007 May 11;356(3):668-73. Epub 2007 Mar 15.

Phosphorylation of threonine 204 of DEAD-box RNA helicase DDX3 by cyclin B/cdc2 in vitro.

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  • 1Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.


DDX3 is a DEAD-box RNA helicase involved in human immunodeficiency virus mRNA export and translation. Previously, we reported that DDX3 is required for cyclin A expression. To examine whether DDX3 is regulated at the post-transcriptional level, we determined the phosphorylation sites of hamster DDX3 in vitro. Threonine 204 (Thr204) is a conserved amino acid residue of DDX3 homologues in yeast, frog, hamster, and human that is located within motif Q of DEAD-box RNA helicases. A Thr204 to Glu204 DDX3 mutant protein lost its function, suggesting that phosphorylation at Thr204 affects DDX3 function. Thr204 was phosphorylated by cyclin B/cdc2. Thr323 in motif Ib was also phosphorylated by cyclin B/cdc2 kinase. We propose a novel function of cyclin B/cdc2 kinase in mitosis, which is to cause a loss of DDX3 function to repress cyclin A expression and to decrease ribosome biogenesis and translation during mitosis.

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