Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.22 (cdc2)
 8,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The nin1-1 mutant of Saccharomyces cerevisiae cannot perform the G1/S and G2/M transitions at restrictive temperatures. At such temperatures, nin1-1 strains fail to activate histone H1 kinase after release from alpha factor-imposed G1 block and after release from hydroxyurea-imposed S block. The nin1-1 mutation shows synthetic lethality with certain cdc28 mutant alleles such as cdc28-IN. Two lines of evidence indicate that Nin1p is a component of the 26S proteasome complex: (i) Nin1p, as well as the known component of the 26S proteasome, shifted to the 26S proteasome peak in the glycerol density gradient after preincubation of crude extract with ATP-Mg2+, and (ii) nin1-1 cells accumulated polyubiquitinated proteins under restrictive conditions. These results suggest that activation of Cdc28p kinase requires proteolysis. We have cloned a human cDNA encoding a regulatory subunit of the 26S proteasome, p31, which was found to be a homolog of Nin1p.
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PMID:Nin1p, a regulatory subunit of the 26S proteasome, is necessary for activation of Cdc28p kinase of Saccharomyces cerevisiae. 762 25

The ubiquitin-mediated degradation of mitotic cyclins is required for cells to exit from mitosis. Previous work with cell-free systems has revealed four components required for cyclin-ubiquitin ligation and proteolysis: a nonspecific ubiquitin-activating enzyme E1, a soluble fraction containing a ubiquitin carrier protein activity called E2-C, a crude particulate fraction containing a ubiquitin ligase (E3) activity that is activated during M-phase, and a constitutively active 26S proteasome that degrades ubiquitinated proteins. Here, we identify a novel approximately 1500-kDa complex, termed the cyclosome, which contains a cyclin-selective ubiquitin ligase activity, E3-C. E3-C is present but inactive during interphase; it can be activated in vitro by the addition of cdc2, enabling the transfer of ubiquitin from E2-C to cyclin. The kinetics of E3-C activation suggest the existence of one or more intermediates between cdc2 and E3-C. Cyclosome-associated E3-C acts on both cyclin A and B, and requires the presence of wild-type N-terminal destruction box motifs in each cyclin. Ubiquitinated cyclins are then rapidly recognized and degraded by the proteasome. These results identify the cyclosome-associated E3-C as the component of the cyclin destruction machinery whose activity is ultimately regulated by cdc2 and, as such, the element directly responsible for setting mitotic cyclin levels during early embryonic cell cycles.
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PMID:The cyclosome, a large complex containing cyclin-selective ubiquitin ligase activity, targets cyclins for destruction at the end of mitosis. 778 45

Cyclin E is a mammalian G1 cyclin that is both required and rate limiting for entry into S phase. The expression of cyclin E is periodic, peaking at the G1-S transition and then decaying as S phase progresses. To understand the mechanisms underlying cyclin E periodicity, we have investigated the regulation of cyclin E degradation. We find that cyclin E is degraded by the ubiquitin-proteasome system, and that this degradation is regulated by both cdk2 binding and cdk2 catalytic activity. Free cyclin E is readily ubiquitinated and degraded by the proteasome. Binding to cdk2 protects cyclin E from ubiquitination, and this protection is reversed by cdk2 activity in a process that involves phosphorylation of cyclin E itself. The data are most consistent with a model in which cdk2 activity initiates cyclin E degradation by promoting the disassembly of cyclin E-cdk2 complexes, followed by the ubiquitination and degradation of free cyclin E.
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PMID:Turnover of cyclin E by the ubiquitin-proteasome pathway is regulated by cdk2 binding and cyclin phosphorylation. 876 42

The 26S proteasome is a large multisubunit protease complex, the largest regulatory subunit of which is a component named p112. Molecular cloning of cDNA encoding human p112 revealed a polypeptide predicted to have 953 amino acid residues and a molecular mass of 105,865. The human p112 gene was mapped to the q37.1-q37.2 region of chromosome 2. Computer analysis showed that p112 has strong similarity to the Saccharomyces cerevisiae Sen3p, which has been listed in a gene bank as a factor affecting tRNA splicing endonuclease. The SEN3 also was identified in a synthetic lethal screen with the nin1-1 mutant, a temperature-sensitive mutant of NIN1. NIN1 encodes p31, another regulatory subunit of the 26S proteasome, which is necessary for activation of Cdc28p kinase. Disruption of the SEN3 did not affect cell viability, but led to temperature-sensitive growth. The human p112 cDNA suppressed the growth defect at high temperature in a SEN3 disruptant, indicating that p112 is a functional homologue of the yeast Sen3p. Maintenance of SEN3 disruptant cells at the restrictive temperature resulted in a variety of cellular dysfunctions, including defects in proteolysis mediated by the ubiquitin pathway, in the N-end rule system, in the stress response upon cadmium exposure, and in nuclear protein transportation. The functional abnormality induced by SEN3 disruption differs considerably from various phenotypes shown by the nin1-1 mutation, suggesting that these two regulatory subunits of the 26S proteasome play distinct roles in the various processes mediated by the 26S proteasome.
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PMID:CDNA cloning of p112, the largest regulatory subunit of the human 26s proteasome, and functional analysis of its yeast homologue, sen3p. 881 93

E2F-1 plays a crucial role in the regulation of cell-cycle progression at the G1-S transition. In keeping with the fact that, when overproduced, it is both an oncoprotein and a potent inducer of apoptosis, its transcriptional activity is subject to multiple controls. Among them are binding by the retinoblastoma gene product (pRb), activation by cdk3, and S-phase-dependent down-regulation of DNA-binding capacity by cyclin A-dependent kinase. Here we report that E2F-1 is actively degraded by the ubiquitin-proteasome pathway. Efficient degradation depends on the availability of selected E2F-1 sequences. Unphosphorylated pRb stabilized E2F-1, protecting it from in vivo degradation. pRb-mediated stabilization was not an indirect consequence of G1 arrest, but rather depended on the ability of pRb to interact physically with E2F-1. Thus, in addition to binding E2F-1 and transforming it into a transcriptional repressor, pRb has another function, protection of E2F-1 from efficient degradation during a period when pRb/E2F complex formation is essential to regulating the cell cycle. In addition, there may be a specific mechanism for limiting free E2F-1 levels, failure of which could compromise cell survival and/or homeostasis.
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PMID:The retinoblastoma gene product protects E2F-1 from degradation by the ubiquitin-proteasome pathway. 895 96

Nin1p, a component of the 26S proteasome of Saccharomyces cerevisiae, is required for activation of Cdc28p kinase at the G1-S-phase and G2-M boundaries. By exploiting the temperature-sensitive phenotype of the nin1-1 mutant, we have screened for genes encoding proteins with related functions to Nin1p and have cloned and characterized two new multicopy suppressors, SUN1 and SUN2, of the nin1-1 mutation. SUN1 can suppress a null nin1 mutation, whereas SUN2, an essential gene, does not. Sun1p is a 268-amino acid protein which shows strong similarity to MBP1 of Arabidopsis thaliana, a homologue of the S5a subunit of the human 26S proteasome. Sun1p binds ubiquitin-lysozyme conjugates as do S5a and MBP1. Sun2p (523 amino acids) was found to be homologous to the p58 subunit of the human 26S proteasome. cDNA encoding the p58 component was cloned. Furthermore, expression of a derivative of p58 from which the N-terminal 150 amino acids had been removed restored the function of a null allele of SUN2. During glycerol density gradient centrifugation, both Sun1p and Sun2p comigrated with the known proteasome components. These results, as well as other structural and functional studies, indicate that both Sun1p and Sun2p are components of the regulatory module of the yeast 26S proteasome.
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PMID:Yeast counterparts of subunits S5a and p58 (S3) of the human 26S proteasome are encoded by two multicopy suppressors of nin1-1. 901 4

We previously presented evidence that a Z-Phe-Ser-argininal-susceptible protease which is involved in oocyte maturation of the starfish, Asterina pectinifera is the proteasome (Takagi Sawada et al, Dev. Biol. 150, 414-418 (1992)). In the present study, we investigated the timing of the function of and the role of the protease in oocyte maturation using Z-Phe-Ser-argininal. By adding the inhibitor in maturing oocytes at various times after 1-methyladenine treatment, the inhibitory ability was markedly reduced in half the time required for germinal vesicle breakdown. Furthermore, the inhibitor potently blocked the activation of histone H1 kinase and the dephosphorylation of cdc2 kinase during oocyte maturation. These results indicate that the Z-Phe-Ser-argininal-susceptible protease, probably the proteasome, plays a key role in the step of the signal transduction pathway that triggers the dephosphorylation of cdc2 kinase in response to the maturation-inducing hormone.
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PMID:Protease triggers dephosphorylation of cdc2 kinase during starfish oocyte maturation. 913 20

In fission yeast, maintenance of genome ploidy is controlled by at least two mechanisms. One operates through the Cdc2/Cdc13 kinase, which also involves the CDK inhibitor Rum1, and the other through the S-phase regulator Cdc18. By screening for sterile mutants that show increased ploidy, we have identified a new gene, pop1+, in mutants that become polyploid. The pop1 mutation shows a synthetic lethal interaction with the temperature-sensitive cdc2 or cdc13 mutation. In a pop1 mutant Rum1 and Cdc18 proteins become accumulated to high levels. The high ploidy phenotype in the pop1 mutant is dependent on the presence of the rum1+ gene, whereas the accumulation of Cdc18 is independent of Rum1. The predicted sequence of the Pop1 protein indicates that it belongs to a WD-repeat family with highest homology to budding yeast Cdc4, which participates in the ubiquitin-dependent pathway. Consistent with this notion, in a mutant of the 26S proteasome, higher molecular weight forms of Rum1 and Cdc18 are accumulated corresponding to polyubiquitination of these proteins. In the pop1 mutant, however, no ubiquitinated forms of these proteins are detected. Finally we show that Pop1 binds Cdc18 in vivo. We propose that Pop1 functions as a recognition factor for Rum1 and Cdc18, which are subsequently ubiquitinated and targeted to the 26S proteasome for degradation.
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PMID:Fission yeast WD-repeat protein pop1 regulates genome ploidy through ubiquitin-proteasome-mediated degradation of the CDK inhibitor Rum1 and the S-phase initiator Cdc18. 920 81

Starfish oocyte maturation was blocked by the addition of 100 microM MG115, a potent proteasome inhibitor, whereas no inhibition was observed by membrane permeable cysteine protease inhibitor, E-64-d. The inhibition by MG115 was diminished by adding at a time corresponding to the half time required for germinal vesicle breakdown. Potent inhibition of germinal vesicle breakdown was also observed by microinjection of anti-proteasome-a-subunit antibodies. The antibody-injected oocytes failed to activate pre-maturation promoting factor (pre-MPF), since the dephosphorylation of phospho-Tyr15 in cdc2 kinase was not observed even in the presence of 1-methyadenine, a maturation-inducing hormone. These results indicate that the proteasome triggers the activation of pre-MPF via the dephosphorylation of cdc2 kinase in the signal transduction pathway in response to the hormonal stimulus during starfish oocyte maturation.
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PMID:The proteasome is an essential mediator of the activation of pre-MPF during starfish oocyte maturation. 922 22

Immediately before the transition from metaphase to anaphase, the protein kinase activity of maturation or M-phase promoting factor (MPF) is inactivated by a mechanism that involves the degradation of its regulatory subunit, cyclin B. The availability of biologically active goldfish cyclin B produced in Escherichia coli and purified goldfish proteasomes (a nonlysosomal large protease) has allowed the role of proteasomes in the regulation of cyclin degradation to be examined for the first time. The 26S, but not the 20S proteasome, digested recombinant 49-kD cyclin B at lysine 57 (K57), producing a 42-kD truncated form. The 42-kD cyclin was also produced by the digestion of native cyclin B forming a complex with cdc2, a catalytic subunit of MPF, and a fragment transiently appeared during cyclin degradation when eggs were released from metaphase II arrest by egg activation. Mutant cyclin at K57 was resistant to both digestion by the 26S proteasome and degradation at metaphase/anaphase transition in Xenopus egg extracts. The results of this study indicate that the destruction of cyclin B is initiated by the ATP-dependent and ubiquitin-independent proteolytic activity of 26S proteasome through the first cutting in the NH2 terminus of cyclin (at K57 in the case of goldfish cyclin B). We also surmise that this cut allows the cyclin to be ubiquitinated for further destruction by ubiquitin-dependent activity of the 26S proteasome that leads to MPF inactivation.
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PMID:Initiation of cyclin B degradation by the 26S proteasome upon egg activation. 929 86


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