Factors controlling cyclin B expression.
Cyclins control the transition between the phases of the eukaryotic cell cycle as regulatory subunits of the cyclin-dependent kinases (CDKs). Phase-specific activation of the CDK is in part regulated by phase-specific expression of their cyclin component. In most eukaryotic cells including higher plant, B-type cyclin genes are expressed specifically at G2/M phase during the cell cycle. Promoters from yeast, plant and animal B-type cyclin genes are all activated in a cell cycle-regulated manner. In yeast, a transcription factor, Mcm1, in cooperation with an uncloned factor SFF, regulates the cell cycle-dependent promoter activation of mitotic B-type cyclin genes, CLB1 and CLB2. Activity of the human cyclin B1 promoter is regulated by a complex mechanism involving multiple cis-acting elements, none of which are sufficient for G2/M-specific promoter activation. In contrast, plants employ a simple mechanism for cell cycle-regulated promoter activation of B-type cyclin genes. Plant B-type cyclin gene promoters contain a common cis-acting element, called the MSA element, which is necessary and sufficient for the phase-specific promoter activation. MSA-like sequences are also found in the promoters of G2/M-specific genes encoding kinesin-like proteins, suggesting that a defined set of G2/M-specific genes are co-regulated by a common MSA-mediated mechanism in plants. Thus, the molecular mechanisms regulating B-type cyclin gene expression are evolutionarily divergent, and the MSA-mediated mechanism seems to be specific to plants. The consensus sequence of the MSA element resembles the binding sites of animal Myb transcription factors. A set of our data suggest the possibility that plant Myb may have unexpected roles in G2/M by inducing B-type cyclin genes, together with other cell cycle-related genes in plants.
Ito
M
M
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Japan.
D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle; D019926:Cyclin B / Q000235:genetics* / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008969:Molecular Sequence Data; D010802:Phylogeny; D010944:Plants / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D016415:Sequence Alignment; D015003:Yeasts / Q000235:genetics / Q000378:metabolism
D019926:Cyclin B; D018844:Cyclin-Dependent Kinases