RESUMO
The mitotic checkpoint acts to inhibit entry into anaphase until all chromosomes have successfully attached to spindle microtubules. Unattached kinetochores are believed to release an activated form of Mad2 that inhibits APC/C-dependent ubiquitination and subsequent proteolysis of components needed for anaphase onset. Using Xenopus egg extracts, a vertebrate homolog of yeast Mps1p is shown here to be a kinetochore-associated kinase, whose activity is necessary to establish and maintain the checkpoint. Since high levels of Mad2 overcome checkpoint loss in Mps1-depleted extracts, Mps1 acts upstream of Mad2-mediated inhibition of APC/C. Mps1 is essential for the checkpoint because it is required for recruitment and retention of active CENP-E at kinetochores, which in turn is necessary for kinetochore association of Mad1 and Mad2.
Assuntos
Proteínas de Transporte , Proteínas de Ciclo Celular , Ciclo Celular/fisiologia , Cinetocoros/metabolismo , Mitose/fisiologia , Oócitos/fisiologia , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Tirosina Quinases/metabolismo , Proteínas de Saccharomyces cerevisiae , Proteínas de Xenopus/metabolismo , Sequência de Aminoácidos , Animais , Proteínas de Ligação ao Cálcio/metabolismo , Núcleo Celular/fisiologia , Proteínas Cromossômicas não Histona/metabolismo , Ciclina B/genética , Ciclina B/metabolismo , Ciclina B1 , Feminino , Proteínas Fúngicas/metabolismo , Humanos , Proteínas Mad2 , Masculino , Meiose , Metáfase , Mitose/efeitos dos fármacos , Modelos Biológicos , Dados de Sequência Molecular , Nocodazol/farmacologia , Proteínas Nucleares , Oócitos/citologia , Oócitos/efeitos dos fármacos , Proteínas Quinases/metabolismo , Proteínas Serina-Treonina Quinases/genética , Proteínas Tirosina Quinases/genética , Proteínas Recombinantes/metabolismo , Reticulócitos/metabolismo , Saccharomyces cerevisiae/citologia , Saccharomyces cerevisiae/enzimologia , Espermatozoides/fisiologia , Ubiquitinas/metabolismo , Vertebrados , Proteínas de Xenopus/genética , Xenopus laevisAssuntos
Proteínas de Ciclo Celular , Proteínas de Neoplasias , Proteínas Nucleares/fisiologia , Fosfoproteínas , Fuso Acromático/metabolismo , Animais , Antígenos Nucleares , Humanos , Carioferinas , Proteínas Associadas aos Microtúbulos/metabolismo , Proteínas Associadas aos Microtúbulos/fisiologia , Proteínas Associadas à Matriz Nuclear , Proteínas Nucleares/metabolismo , Proteína ran de Ligação ao GTP/metabolismo , Proteína ran de Ligação ao GTP/fisiologiaAssuntos
Proteínas de Ciclo Celular , Núcleo Celular/metabolismo , Fatores de Troca do Nucleotídeo Guanina , Microtúbulos/metabolismo , Proteínas de Neoplasias , Proteínas Nucleares/metabolismo , Fosfoproteínas , Fuso Acromático/metabolismo , Proteínas de Xenopus , Transporte Ativo do Núcleo Celular , Animais , Compartimento Celular , Centrossomo/metabolismo , Cromatina/metabolismo , Citoplasma/metabolismo , Proteínas de Ligação a DNA/metabolismo , Interfase , Carioferinas , Meiose , Proteínas Associadas aos Microtúbulos/metabolismo , Mitose , Membrana Nuclear/metabolismo , Xenopus , Proteína ran de Ligação ao GTP/metabolismoRESUMO
Fluorescent molecules serve as valuable tools for the detection of a variety of biochemical phenomena. Such reagents have been employed for protein localization, quantitation of gene expression, detection of nucleic acids, cell sorting, and determination of chemical concentrations. Although fluorescence is a useful tool for detecting molecules within cells, its application in vivo has been limited. The ideal vital fluorescent tag should (1) be detectable without causing cytological damage, (2) be able to label a wide variety of cell types readily, and (3) be able to be targeted to virtually any subcellular region. The recently cloned green fluorescent protein (GFP) from the jellyfish Aequorea victoria is such a molecule. This overview describes the use of this proteinaceous fluorophore for in vivo observation of cellular phenomena, including applications and problems with the use of GFP, a discussion of mutant GFPs with altered fluorescence characteristics, and also some details on microscopy requirements.
Assuntos
Proteínas de Fluorescência Verde/metabolismo , Hidrozoários/metabolismo , Proteínas/análise , Animais , Fluorescência , Proteínas de Fluorescência Verde/análise , Hidrozoários/químicaRESUMO
Fluorescent molecules serve as valuable tools for the detection of a variety of biochemical phenomena. Such reagents have been employed for protein localization, quantitation of gene expression, detection of nucleic acids, cell sorting, and determination of chemical concentrations. Although fluorescence is a useful tool for detecting molecules within cells, its application in vivo has heretofore been limited. The ideal vital fluorescent tag should (1) be detectable without causing cytological damage, (2) be able to label a wide variety of cell types readily, and (3) be able to be targeted to virtually any subcellular region. The recently cloned green fluorescent protein (GFP) from the jellyfish Aequorea victoria is such a molecule. This overview describes the use of this proteinaceous fluorophore for in vivo observation of cellular phenomena, including applications and problems with the use of GFP, a discussion of mutant GFPs with altered fluorescence characteristics, and also some details on microscopy requirements.
Assuntos
DNA Complementar/genética , Proteínas de Fluorescência Verde/análise , Equorina , Animais , Genes Reporter , Vetores Genéticos , Proteínas de Fluorescência Verde/química , Proteínas de Fluorescência Verde/genética , Luminescência , Mutação , Proteínas Recombinantes/análise , Saccharomyces cerevisiae/genéticaRESUMO
Fluorescent molecules serve as valuable tools for the detection of numerous biochemical phenomena and have been employed for protein localization, quantitation of gene expression, detection of nucleic acids, cell sorting and determination of chemical concentrations. However, the use of such techniques generally requires significant nonphysiological perturbations to the biological system being studied; therefore, they are not always appropriate for the observation of dynamic phenomena. Green fluorescent protein (GFP), cloned from jellyfish, has been used to overcome many of these problems. It is a small, extremely stable fluorescent protein that has been successfully expressed and detected in a wide variety of organisms, both in intact form and fused to other proteins. This overview unit describes the use of this proteinaceous fluorophore for in vivo observation of cellular phenomena.
Assuntos
Técnicas Genéticas , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Proteínas/química , Animais , Proteínas de Fluorescência Verde/biossíntese , Microscopia de Fluorescência/métodos , Mutação , Proteínas/genética , Proteínas/metabolismo , Cifozoários/química , Cifozoários/genéticaRESUMO
Accurate chromatid separation is monitored by a checkpoint mechanism that delays anaphase onset until all centromeres are correctly attached to the mitotic spindle. Using Xenopus egg extracts, the kinetochore-associated microtubule motor protein CENP-E is now found to be required for establishing and maintaining this checkpoint. When CENP-E function is disrupted by immunodepletion or antibody addition, extracts fail to arrest in response to spindle damage. Mitotic arrest can be restored by addition of high levels of soluble MAD2, demonstrating that the absence of CENP-E eliminates kinetochore-dependent signaling but not the downstream steps in checkpoint signal transduction. Because it directly binds both to spindle microtubules and to the kinetochore-associated checkpoint kinase BUBR1, CENP-E is a central component in the vertebrate checkpoint that modulates signaling activity in a microtubule-dependent manner.
Assuntos
Proteínas de Transporte , Proteínas Cromossômicas não Histona/metabolismo , Cinetocoros/fisiologia , Mitose/fisiologia , Animais , Anticorpos/farmacologia , Proteínas de Ligação ao Cálcio/farmacologia , Proteínas de Ciclo Celular , Cromátides/fisiologia , Proteínas Cromossômicas não Histona/genética , Proteínas Cromossômicas não Histona/imunologia , Proteínas Fúngicas/farmacologia , Histonas/metabolismo , Técnicas In Vitro , Mitose/efeitos dos fármacos , Testes de Neutralização , Proteínas Nucleares , Oócitos/fisiologia , Fosforilação , Proteínas Recombinantes/farmacologia , Transdução de Sinais/fisiologia , XenopusRESUMO
We find that the peripheral ER in Saccharomyces cerevisiae forms a dynamic network of interconnecting membrane tubules throughout the cell cycle, similar to the ER in higher eukaryotes. Maintenance of this network does not require microtubule or actin filaments, but its dynamic behavior is largely dependent on the actin cytoskeleton. We isolated three conditional mutants that disrupt peripheral ER structure. One has a mutation in a component of the COPI coat complex, which is required for vesicle budding. This mutant has a partial defect in ER segregation into daughter cells and disorganized ER in mother cells. A similar phenotype was found in other mutants with defects in vesicular trafficking between ER and Golgi complex, but not in mutants blocked at later steps in the secretory pathway. The other two mutants found in the screen have defects in the signal recognition particle (SRP) receptor. This receptor, along with SRP, targets ribosome-nascent chain complexes to the ER membrane for protein translocation. A conditional mutation in SRP also disrupts ER structure, but other mutants with translocation defects do not. We also demonstrate that, both in wild-type and mutant cells, the ER and mitochondria partially coalign, and that mutations that disrupt ER structure also affect mitochondrial structure. Our data suggest that both trafficking between the ER and Golgi complex and ribosome targeting are important for maintaining ER structure, and that proper ER structure may be required to maintain mitochondrial structure.
Assuntos
Complexo I de Proteína do Envoltório/genética , Retículo Endoplasmático/ultraestrutura , Mutação , Receptores Citoplasmáticos e Nucleares/genética , Receptores de Peptídeos/genética , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/genética , Proteínas de Transporte Vesicular , Actinas , Transporte Biológico , Vesículas Revestidas pelo Complexo de Proteína do Envoltório , Citoesqueleto , Retículo Endoplasmático/genética , Retículo Endoplasmático/metabolismo , Proteínas Fúngicas/genética , Proteínas Ativadoras de GTPase , Complexo de Golgi/metabolismo , Proteínas de Membrana/genética , Microtúbulos , Mitocôndrias/ultraestrutura , Proteínas SNARE , Saccharomyces cerevisiae/ultraestrutura , Partícula de Reconhecimento de Sinal/metabolismoAssuntos
Núcleo Celular/metabolismo , Proteínas de Ligação ao GTP/metabolismo , Guanosina Trifosfato/metabolismo , Proteínas Nucleares/metabolismo , Fuso Acromático/metabolismo , Animais , Transporte Biológico , Ciclo Celular , Microtúbulos/metabolismo , Modelos Biológicos , Xenopus laevis , Proteína ran de Ligação ao GTPRESUMO
We have identified a novel centromere-associated gene product from Saccharomyces cerevisiae that plays a role in spindle assembly and stability. Strains with a deletion of SLK19 (synthetic lethal Kar3p gene) exhibit abnormally short mitotic spindles, increased numbers of astral microtubules, and require the presence of the kinesin motor Kar3p for viability. When cells are deprived of both Slk19p and Kar3p, rapid spindle breakdown and mitotic arrest is observed. A functional fusion of Slk19p to green fluorescent protein (GFP) localizes to kinetochores and, during anaphase, to the spindle midzone, whereas Kar3p-GFP was found at the nuclear side of the spindle pole body. Thus, these proteins seem to play overlapping roles in stabilizing spindle structure while acting from opposite ends of the microtubules.
Assuntos
Centrômero/metabolismo , Proteínas Fúngicas/metabolismo , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/citologia , Fuso Acromático/metabolismo , Anáfase , Núcleo Celular/metabolismo , Citoplasma/metabolismo , Proteínas Fúngicas/genética , Genes Letais , Cinesinas , Cinetocoros/metabolismo , Microscopia de Fluorescência , Proteínas Associadas aos Microtúbulos/genética , Proteínas Associadas aos Microtúbulos/metabolismo , Microtúbulos/metabolismo , Mitose , Mutação , Ácido Orótico/análogos & derivados , Fenótipo , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismoRESUMO
Although vertebrate cytoplasmic dynein can move to the minus ends of microtubules in vitro, its ability to translocate purified vesicles on microtubules depends on the presence of an accessory complex known as dynactin. We have cloned and characterized a novel gene, NIP100, which encodes the yeast homologue of the vertebrate dynactin complex protein p150(glued). Like strains lacking the cytoplasmic dynein heavy chain Dyn1p or the centractin homologue Act5p, nip100Delta strains are viable but undergo a significant number of failed mitoses in which the mitotic spindle does not properly partition into the daughter cell. Analysis of spindle dynamics by time-lapse digital microscopy indicates that the precise role of Nip100p during anaphase is to promote the translocation of the partially elongated mitotic spindle through the bud neck. Consistent with the presence of a true dynactin complex in yeast, Nip100p exists in a stable complex with Act5p as well as Jnm1p, another protein required for proper spindle partitioning during anaphase. Moreover, genetic depletion experiments indicate that the binding of Nip100p to Act5p is dependent on the presence of Jnm1p. Finally, we find that a fusion of Nip100p to the green fluorescent protein localizes to the spindle poles throughout the cell cycle. Taken together, these results suggest that the yeast dynactin complex and cytoplasmic dynein together define a physiological pathway that is responsible for spindle translocation late in anaphase.
Assuntos
Anáfase/fisiologia , Dineínas/fisiologia , Proteínas Fúngicas/fisiologia , Proteínas Associadas aos Microtúbulos/fisiologia , Fuso Acromático/fisiologia , Sequência de Aminoácidos , Anáfase/genética , Animais , Complexo Dinactina , Dineínas/química , Proteínas Fúngicas/genética , Proteínas Fúngicas/isolamento & purificação , Proteínas Associadas aos Microtúbulos/química , Proteínas Associadas aos Microtúbulos/genética , Proteínas Associadas aos Microtúbulos/isolamento & purificação , Dados de Sequência Molecular , Ratos , Saccharomyces cerevisiae , Proteínas de Saccharomyces cerevisiae , Homologia de Sequência de Aminoácidos , Fuso Acromático/genéticaRESUMO
We describe the use of time-lapse fluorescence microscopy to visualize the movement of the DNA replication origin and terminus regions on the Bacillus subtilis chromosome during the course of the cell cycle. The origin and terminus regions were tagged with a cassette of tandem lac operator repeats and visualized through the use of a fusion of the green fluorescent protein to the LacI repressor. We have discovered that origin regions abruptly move apart towards the cell poles during a brief interval of the cell cycle. This movement was also seen in the absence of cell wall growth and in the absence of the product of the parB homologue spo0J. The origin regions moved apart an average distance of 1.4 microm in an 11 min period of abrupt movement, representing an average velocity of 0.17 microm min(-1), and reaching a maximum velocity of greater than 0.27 microm min(-1). The terminus region also exhibited a striking pattern of movement but not as far or a rapid as the origin region. These results provide evidence for a mitotic-like motor that is responsible for segregation of the origin regions of the chromosomes.
Assuntos
Bacillus subtilis/genética , Cromossomos Bacterianos/ultraestrutura , DNA Bacteriano/ultraestrutura , Origem de Replicação , Fator sigma , Fatores de Transcrição , Proteínas de Bactérias/genética , Ciclo Celular , Parede Celular , Processamento de Imagem Assistida por Computador , Microscopia de Fluorescência , MutagêneseRESUMO
In the budding yeast Saccharomyces cerevisiae, the spindle pole body (SPB) serves as the microtubule-organizing center and is the functional analog of the centrosome of higher organisms. By expressing a fusion of a yeast SPB-associated protein to the Aequorea victoria green fluorescent protein, the movement of the SPBs in living yeast cells undergoing mitosis was observed by fluorescence microscopy. The ability to visualize SPBs in vivo has revealed previously unidentified mitotic events. During anaphase, the mitotic spindle has four sequential activities: alignment at the mother-daughter junction, fast elongation, translocation into the bud, and slow elongation. These results indicate that distinct forces act upon the spindle at different times during anaphase.