Phosphorylation of threonine 204 of DEAD-box RNA helicase DDX3 by cyclin B/cdc2 in vitro.
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.
Sekiguchi
Takeshi
T
Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. sekigu@molbiol.med.kyushu-u.ac.jp
Kurihara
Yoshiko
Y
Fukumura
Junko
J
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D006224:Cricetinae; D019926:Cyclin B / Q000378:metabolism*; D053487:DEAD-box RNA Helicases / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology; D008969:Molecular Sequence Data; D010766:Phosphorylation; D013912:Threonine / Q000378:metabolism*
D019926:Cyclin B; D013912:Threonine; D016203:CDC2 Protein Kinase; D053487:DEAD-box RNA Helicases