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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The protein kinase activity of the cell cycle regulator p34cdc2 is inactivated when the mitotic cyclin to which it is bound is degraded. The amino (N)-terminus of mitotic cyclins includes a conserved "destruction box" sequence that is essential for degradation. Although the N-terminus of sea urchin cyclin B confer cell cycle-regulated degradation to a fusion protein, a truncated protein containing only the N-terminus of Xenopus cyclin B2, including the destruction box, is stable under conditions where full length molecules are degraded. In an attempt to identify regions of cyclin B2, other than the destruction box, involved in degradation, the stability of proteins encoded by C-terminal deletion mutants of cyclin B2 was examined in Xenopus egg extracts. Truncated cyclin with only the first 90 amino acids was stable, but other C-terminal deletions lacking between 14 and 187 amino acids were unstable and were degraded by a mechanism that was neither cell cycle regulated nor dependent upon the destruction box. None of the C-terminal deletion mutants bound p34cdc2. To investigate whether the binding of p34cdc2 is required for cell cycle-regulated degradation, the behavior of proteins encoded by a series of full length Xenopus cyclin B2 cDNA with point mutations in conserved amino acids in the p34cdc2-binding domain was examined. All of the point mutants failed to form stable complexes with p34cdc, and their degradation was markedly reduced compared to wild-type cyclin. Similar results were obtained when the mutant cyclins were synthesized in reticulocyte lysates and when cyclin mRNA was translated directly in a Xenopus egg extract. These results indicate that mutations that interfere with p34cdc2 binding also interfere with cyclin destruction, suggesting that p34cdc2 binding is required for the cell cycle-regulated destruction of Xenopus cyclin B2.
Mol Biol Cell 1994 Jul
PMID:Cell cycle-regulated degradation of Xenopus cyclin B2 requires binding to p34cdc2. 781 41

Cln3 cyclin of the budding yeast Saccharomyces cerevisiae is a key regulator of Start, a cell cycle event in G1 phase at which cells become committed to division. The time of Start is sensitive to Cln3 levels, which in turn depend on the balance between synthesis and rapid degradation. Here we report that the breakdown of Cln3 is ubiquitin dependent and involves the ubiquitin-conjugating enzyme Cdc34 (Ubc3). The C-terminal tail of Cln3 functions as a transferable signal for degradation. Sequences important for Cln3 degradation are spread throughout the tail and consist largely of PEST elements, which have been previously suggested to target certain proteins for rapid turnover. The Cln3 tail also appears to contain multiple phosphorylation sites, and both phosphorylation and degradation of Cln3 are deficient in a cdc28ts mutant at the nonpermissive temperature. A point mutation at Ser-468, which lies within a Cdc28 kinase consensus site, causes approximately fivefold stabilization of a Cln3-beta-galactosidase fusion protein that contains a portion of the Cln3 tail and strongly reduces the phosphorylation of this protein. These data indicate that the degradation of Cln3 involves CDC28-dependent phosphorylation events.
Mol Cell Biol 1995 Feb
PMID:p34Cdc28-mediated control of Cln3 cyclin degradation. 782 41

Developing thymocytes and some T-cell hybridomas undergo activation-dependent programmed cell death. Although recent studies have identified some critical regulators in programmed cell death, the role of cell cycle regulation in activation-induced cell death in T cells has not been addressed. We demonstrate that synchronized T-cell hybridomas, irrespective of the point in the cell cycle at which they are activated, stop cycling shortly after they reach G2/M. These cells exhibit the diagnostic characteristics of apoptotic cell death. Although p34cdc2 levels are not perturbed after activation of synchronously cycling T cells, cyclin B- and p34cdc2-associated histone H1 kinase activity is persistently elevated. This activation-dependent induction of H1 kinase activity in T cells is associated with a decrease in the phosphotyrosine content of p34cdc2. We also demonstrate that transient inappropriate coexpression of cyclin B with p34cdc2 induces DNA fragmentation in a heterologous cell type. Finally, in T cells, cyclin B-specific antisense oligonucleotides suppress activation-induced cell death but not cell death induced by exposure to dexamethasone. We therefore conclude that a persistent elevation of the level of cyclin B kinase is required for activation-induced programmed T-cell death.
Mol Cell Biol 1995 Feb
PMID:Activation-induced T-cell death is cell cycle dependent and regulated by cyclin B. 782 58

In the budding yeast Saccharomyces cerevisiae, progress of the cell cycle beyond the major control point in G1 phase, termed START, requires activation of the evolutionarily conserved Cdc28 protein kinase by direct association with G1 cyclins. We have used a conditional lethal mutation in CDC28 of S. cerevisiae to clone a functional homologue from the human fungal pathogen Candida albicans. The protein sequence, deduced from the nucleotide sequence, is 79% identical to that of S. cerevisiae Cdc28 and as such is the most closely related protein yet identified. We have also isolated from C. albicans two genes encoding putative G1 cyclins, by their ability to rescue a conditional G1 cyclin defect in S. cerevisiae; one of these genes encodes a protein of 697 amino acids and is identical to the product of the previously described CCN1 gene. The second gene codes for a protein of 465 residues, which has significant homology to S. cerevisiae Cln3. These data suggest that the events and regulatory mechanisms operating at START are highly conserved between these two organisms.
Mol Gen Genet 1994 Dec 15
PMID:Molecular cloning and analysis of CDC28 and cyclin homologues from the human fungal pathogen Candida albicans. 783 Jul 19

In cells of higher eukaryotic organisms the activity of the p34cdc2/cyclin B complex is inhibited by phosphorylation of p34cdc2 at two sites within its amino-terminus (threonine 14 and tyrosine 15). In this study, the cell cycle regulation of the kinases responsible for phosphorylating p34cdc2 on Thr14 and Tyr15 was examined in extracts prepared from both HeLa cells and Xenopus eggs. Both Thr14- and Tyr15- specific kinase activities were regulated in a cell cycle-dependent manner. The kinase activities were high throughout interphase and diminished coincident with entry of cells into mitosis. In HeLa cells delayed in G2 by the DNA-binding dye Hoechst 33342, Thr14- and Tyr15-specific kinase activities remained high, suggesting that a decrease in Thr14- and Tyr15- kinase activities may be required for entry of cells into mitosis. Similar cell cycle regulation was observed for the Thr14/Tyr15 kinase(s) in Xenopus egg extracts. These results indicate that activation of CDC2 and entry of cells into mitosis is not triggered solely by activation of the Cdc25 phosphatase but by the balance between Thr14/Tyr15 kinase and phosphatase activities. Finally, we have detected two activities capable of phosphorylating p34cdc2 on Thr14 and/or Tyr15 in interphase extracts prepared from Xenopus eggs. An activity capable of phosphorylating Tyr15 remained soluble after ultracentrifugation of interphase extracts whereas a second activity capable of phosphorylating both Thr14 and Tyr15 pelleted. The pelleted fraction contained activities that were detergent extractable and that phosphorylated p34cdc2 on both Thr14 and Tyr15. The Thr14- and Tyr15-specific kinase activities co-purified through three successive chromatographic steps indicating the presence of a dual-specificity protein kinase capable of acting on p34cdc2.
Mol Biol Cell 1994 Sep
PMID:Cell cycle regulation of the p34cdc2 inhibitory kinases. 784 26

We recently demonstrated that the plant amino acid, mimosine, is an extremely efficacious inhibitor of DNA replication in mammalian cells [P. A. Dijkwel and J. L. Hamlin (1992) Mol. Cell. Biol. 12, 3715-3722; P. J. Mosca et al. (1992) Mol. Cell. Biol. 12, 4375-4383]. Several of its properties further suggested that mimosine might target initiation at origins of replication, which would make it a unique and very useful inhibitor for studying the regulation of DNA synthesis. However, mimosine is known to chelate iron, a cofactor for ribonucleotide reductase. Thus, the possibility arose that mimosine functions in vivo simply by lowering intracellular deoxyribonucleotide pools. In the present study, we show that, in fact, it is possible to override mimosine inhibition in vivo by adding excess iron; however, copper, which is not a substitute for iron in ribonucleotide reductase, is equally effective. Evidence is presented that mimosine functions instead by binding to an intracellular protein. We show that radiolabeled mimosine can be specifically cross-linked to a 50 kDa polypeptide (termed p50) in vitro. Binding to p50 is virtually undetectable in CHO cells selected for resistance to 1 mM mimosine, arguing that p50 is the biologically relevant target. p50 is not associated with the cellular membrane fraction and, hence, is probably not a channel protein. Furthermore, the binding activity does not vary markedly as a function of cell cycle position, arguing that p50 is not a cyclin. Finally, both iron and copper are able to reverse the mimosine-p50 interaction in vitro, probably explaining why both metal ions are able to overcome mimosine's inhibitory effect on DNA synthesis in vivo.
 ...
PMID:Mimosine, a novel inhibitor of DNA replication, binds to a 50 kDa protein in Chinese hamster cells. 786 31

It is widely believed that in mammalian cells the cellular transcription factor (DRTF1/E2F integrates cell-cycle events with the transcription apparatus by interacting with important regulators of the cell cycle, such as the retinoblastoma gene product (pRb) and related proteins, cyclins, and cyclin-dependent kinases. Here, we have defined DRTF1/E2F in Xenopus laevis that, like its mammalian counterpart, specifically binds to the E2F site, is regulated during development, and interacts with pRb and related proteins. We have isolated cDNAs that encode the functional homologue of mammalian DP-1, X1 DP-1, together with a close relative, X1 DP-2. X1 DP-1, which is highly conserved with murine DP-1, is a major DNA binding component of X1 DRTF1/E2F. Both DP-1 and DP-2 synergistically interact with members of the E2F family of proteins, E2F-1, E2F-2, and E2F-3, to generate DNA binding complexes that specifically recognize the E2F site and functionally interact with E2F-1 in E2F site-dependent transcriptional activation of cellular genes. DP-1 and DP-2 encode maternally stored transcripts that are expressed during early development. In the adult however, the expression of DP-1 and DP-2 is tissue restricted. This study therefore defines a new family of transcription factors, the DP proteins, members of which can interact combinatorially with E2F proteins to generate an array of DNA binding complexes that integrate cell-cycle progression with the transcription apparatus through the E2F binding site. The tissue-specific expression of DP family members suggests that the combination of DP/E2F heterodimers that constitute DRTF1/E2F is influenced by the phenotype of the cell.
Mol Biol Cell 1994 Oct
PMID:Molecular characterization of Xenopus laevis DP proteins. 786 76

In the absence of serum, nerve growth factor (NGF) promotes the survival and differentiation of the PC12 pheochromocytoma cell line. In the presence of serum, NGF acts primarily as a differentiation factor and negative regulator of cell cycling. To investigate NGF control of cell cycling, we have analyzed the regulation of cyclin dependent kinases during PC12 cell differentiation. NGF treatment leads to a reduction in the steady-state protein levels of p33cdk2 and p34cdc2, two key regulators of cell cycle progression. The decrease in p33cdk2 and p34cdc2 coincides with a decrease in the enzymatic activity of cyclinA-p34cdc2, cyclinB-p34cdc2, cyclinE-p33cdk2, and cyclinA-p33cdk2 kinases. The decline in p33cdk2 and p34cdc2 kinase activity in response to NGF is accelerated in cells that over-express the p140trk NGF receptor, suggesting that the timing of the down- regulation is dependent on the level of p140trk and the strength of the NGF signal. The level of cyclin A, a regulatory subunit of p33cdk2 and p34cdc2, is relatively constant during PC12 differentiation. Nevertheless, the DNA binding activity of the cyclinA-associated transcription factor E2F/DP decreases. Thus, NGF down-regulates the activity of cyclin dependent kinases and cyclin-transcription factor complexes during PC12 differentiation.
Mol Biol Cell 1994 Nov
PMID:Nerve growth factor regulates the expression and activity of p33cdk2 and p34cdc2 kinases in PC12 pheochromocytoma cells. 786 86

In order to investigate the role of cell division in plant development, we isolated several plant genes which encode homologues of animal and yeast cell cycle regulators known as cyclins. Through the use of degenerate primers and the polymerase chain reaction (PCR) we isolated a Brassica sequence which showed homology to the 'cyclin box' functional domain found within cyclin proteins. Southern blot analysis indicated that Brassica napus has a large number of genes containing cyclin box-related sequences. This was further supported by the isolation of cyclin box sequences from six different genomic clones. In addition, we have isolated two different cyclin cDNA clones, BnCYC1 and BnCYC2, from a Brassica napus shoot apical cDNA library. Both of the cDNA clones contain a 'destruction box' regulatory domain similar to animal mitotic cyclins. Northern blot analysis using BnCYC2 shows mRNA levels which correlate well with the level of cell division in various tissues. Messenger RNA abundance was highest in 1-3 mm leaves, root tips and shoot apices. The mRNA detected using BnCYC1 was restricted to young leaves and the shoot apex, suggesting divergent, organ-specific roles for cyclin family members. The results demonstrate that the plant cyclin gene family is more extensive than previously demonstrated and consists of genes expressed in all dividing tissues as well as a subset of developmentally specific members.
Plant Mol Biol 1995 Jan
PMID:Classification and expression of a family of cyclin gene homologues in Brassica napus. 788 17

The Saccharomyces cerevisiae CLN3 protein, a G1 cyclin, positively regulates the expression of CLN1 and CLN2, two additional G1 cyclins whose expression during late G1 is activated, in part, by the transcription factors SWI4 and SWI6. We isolated 12 complementation groups of mutants that require CLN3. The members of one of these complementation groups have mutations in the BCK2 gene. In a wild-type CLN3 genetic background, bck2 mutants have a normal growth rate but have a larger cell size, are more sensitive to alpha-factor, and have a modest defect in the accumulation of CLN1 and CLN2 RNA. In the absence of CLN3, bck2 mutations cause an extremely slow growth rate: the cells accumulate in late G1 with very low levels of CLN1 and CLN2 RNA. The slow growth rate and long G1 delay of bck2 cln3 mutants are cured by heterologous expression of CLN2. Moreover, overexpression of BCK2 induces very high levels of CLN1, CLN2, and HCS26 RNAs. The results suggest that BCK2 and CLN3 provide parallel activation pathways for the expression of CLN1 and CLN2 during late G1.
Mol Cell Biol 1995 Apr
PMID:Activation of CLN1 and CLN2 G1 cyclin gene expression by BCK2. 789 77


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