Os05g0392300

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Annotated Information

Function

Cyclin-dependent protein kinases (CDKs) play key roles in regulating the eukaryotic cell cycle. Cyclin-dependent kinases (CDKs) are the central components of eukaryotic cell cycle regulation. Cell division is regulated by the sequential activation of cyclin-dependent kinases (CDKs). CDKs are among the most highly regulated enzymes known. In animals and yeast, two classes of CAKs have been identified. They are represented by human p40 MO15/Cdk7 and by Cak1p Civ1 from budding yeast. These CAKs have low homology with each other, and they differ in their enzyme characteristics. Human Cdk7 has been shown to phosphorylate CDK substrates and the C-terminal domain (CTD) of the large subunit of RNA polymerase II, the second reaction as part of the general transcription factor IIH. Because transcription factor IIH also is involved in nucleotide excision repair, Cdk7 may have functions in cell cycle control, in transcriptional regulation, and in DNA repair. Budding yeast Cak1p acts as a CAK but does not display CTD kinase activity. Most CDKs are thought to be activated by CAKs, and CAKs are essential genes. Animal and yeast CAKs are expressed and active throughout the mitotic cell cycle with no change in subcellular localization, indicating that CAKs are not regulated in these organisms. CAK overexpression increased CAK activity but did not produce a mutant phenotype. Yet, CDK phosphorylation appearsto have specific functions in cell cycle regulation. Immunodepletion of Xenopus XlCdk7 in egg extracts suppressed CAK activity and arrested cells before M-phase. Furthermore, Drosophila DmCdk7 was shown toactivate mitotic CDK complexes and was required for mitosis. Also, the fission yeast Cdk7 homolog Mcs6/Crk1/Mop1 was isolated in a screen as a potential mitotic inducer resulting from increased Cdc2 activity. Analysis of a Cak1p mutant from budding yeast showed that 70% of all cells arrested at G1/S and that the remaining cells arrested in G2/M, indicating that this CAK clearly was required for both G1/S and G2/M transitions.

Expression

Cyclin-dependent protein kinases (CDKs) play key roles in regulating the eukaryotic cell cycle. some reports have analyzed the expression of four rice (Oryza sativa) CDK genes, cdc2Os1, cdc2Os2, cdc2Os3,and R2, by in situ hybridization of sections of root apices. Transcripts of cdc2Os1, cdc2Os2, and R2 were detected uniformly in the dividing region of the root apex. cdc2Os1 and cdc2Os2 were also expressed in differentiated cells such as those in the sclerenchyma, pericycle, and parenchyma of the central cylinder. By contrast, signals corresponding to transcripts of cdc2Os3 were distributed only in patches in the dividing region. Counterstaining of sections with 4*,6-diamidino-2-phenylindole and double-target in situ hybridization with a probe for histone H4 transcripts revealed that cdc2Os3 transcripts were abundant from the G2 to the M phase, but were less abundant or absent during the S phase. The levels of the Cdc2Os3 protein and its associated histone H1-kinase activity were reduced by treatment of cultured cells with hydroxyurea, which blocks cycling cells at the onset of the S phase. The results suggest that domains other than the conserved amino acid sequence (the PSTAIRE motif) have important roles in the function of non-PSTAIRE CDKs in distinct cell-cycle phases.

Evolution

Phylogenetic tree for members of the CDK protein family.The tree was constructed using the CLUSTAL software program, with sequences selected from the databases.Rice CDKs are boxed. Amcdc2a-d, CDKs of snapdragon; Cdc2aAt and Cdc2bAt, CDKs of Arabidopsis; Cdc2MsA-F, CDKs of alfalfa;NtCdc2, CDK of tobacco; ZmCdc2, CDK of maize; ScCdc28, Cdc28 of S. cerevisiae; SpCdc2, Cdc2 of S. pombe; Cdk2–7, human CDKs

Labs working on this gene

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References

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