A process independent of the anaphase-promoting complex contributes to instability of the yeast S phase cyclin Clb5

Proteolytic destruction of many cyclins is induced by a multi-subunit ubiquitin ligase termed the anaphase promoting complex/ cyclosome (APC/C). In the budding yeast Saccharomyces cerevisiae, the S phase cyclin Clb5 and the mitotic cyclins Clb1-4 are known as substrates of this complex. The relevance of APC/C in proteolysis of Clb5 is still under debate. Importantly, a deletion of the Clb5 destruction box has little influence on cell cycle progression. To understand Clb5 degradation in more detail, we applied in vivo pulse labeling to determine the half-life of Clb5 at different cell cycle stages and in the presence or absence of APC/C activity. Clb5 is significantly unstable, with a half-life of ∼8-10 min, at cell cycle periods when APC/C is inactive and in mutants impaired in APC/C function. A Clb5 version lacking its cyclin destruction box is similarly unstable. The half-life of Clb5 is further decreased in a destruction box-dependent manner to 3-5 min in mitotic or G 1 cells with active APC/C. Clb5 instability is highly dependent on the function of the proteasome. We conclude that Clb5 proteolysis involves two different modes for targeting of Clb5 to the proteasome, an APC/C-dependent and an APC/C-independent mechanism. These different modes apparently have overlapping functions in restricting Clb5 levels in a normal cell cycle, but APC/C function is essential in the presence of abnormally high Clb5 levels. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc

Abundanz und Artenvielfalt von Schwebfliegen in isolierten Buntbrachen

In der Schweiz werden verschiedene Massnahmen umgesetzt, um die Biodiversität in der Agrarlandschaft zu erhöhen. Ein Mittel dazu sind Biodiversitätsförderflächen, welche durch landwirtschaftliche Betriebe bewirtschaftet werden. In ackerbaulich intensiv genutzten Gebieten ist der Druck auf die Biodiversität besonders gross. Hier können Förderflächen Lebensräume bieten, die Artenvielfalt erhöhen und landwirtschaftliche Nützlinge fördern. In dieser Arbeit wurde die Nützlingsgruppe der Schwebfliegen in den Förderflächen des Typs Buntbrache untersucht. Während drei Feldbegehungen zwischen Mai und August wurden in Buntbrachen des Kantons Aargau Schwebfliegen und Blütendichte erfasst. Gesamthaft konnten 28 Schwebfliegen-Taxa unterschieden werden, wobei die Art Eristalis tenax sowie die Gattung Sphaerophoria stark dominant vertreten waren. Festgestellt wurde ein positiver Zusammenhang von der Blütendichte zur Individuenzahl und Artenzahl. Eine besonders gute Korrelation bestand zwischen Eristalis tenax und den Blüten von Origanum vulgare. Die separate Auswertung von aphidophagen und nicht-aphidophagen Taxa wies darauf hin, dass aphidophage Arten nicht von der umgebenden Landschaftsstruktur im 500 m Radius beeinflusst werden. Die Abundanz von nicht-aphidophagen Arten allerdings verhielt sich negativ zur Distanz von Waldrand & Hecken und leicht positiv zum Anteil Biodiversitätsförderflächen. Die Eignung der untersuchten Buntbrachen zur Förderung von Schwebfliegen als Nützlinge wird gering eingeschätzt. Grund dafür ist die tiefe Blütendichte zu Beginn des Sommers und damit einhergehend tiefer Schwebfliegenabundanz zur Zeit des wichtigsten Schädlingsbefalls

GRAINet: Automatische Kornverteilungsanalysen aus Drohnen-Bildern mit CNNs

Aufsatz veröffentlicht in: "Wasserbau-Symposium 2021: Wasserbau in Zeiten von Energiewende, Gewässerschutz und Klimawandel, Zurich, Switzerland, September 15-17, 2021, Band 2" veröffentlicht unter: https://doi.org/10.3929/ethz-b-00049975

The Human Homologue of Bub3 Is Required for Kinetochore Localization of Bub1 and a Mad3/Bub1-related Protein Kinase

A feedback control mechanism, or cell cycle checkpoint, delays the onset of anaphase until all the chromosomes are correctly aligned on the mitotic spindle. Previously, we showed that the murine homologue of Bub1 is not only required for checkpoint response to spindle damage, but also restrains progression through a normal mitosis (Taylor, S.S., and F. McKeon. 1997. Cell. 89:727–735). Here, we describe the identification of a human homologue of Bub3, a 37-kD protein with four WD repeats. Like Bub1, Bub3 localizes to kinetochores before chromosome alignment. In addition, Bub3 and Bub1 interact in mammalian cells. Deletion mapping was used to identify the domain of Bub1 required for binding Bub3. Significantly, this same domain is required for kinetochore localization of Bub1, suggesting that the role of Bub3 is to localize Bub1 to the kinetochore, thereby activating the checkpoint in response to unattached kinetochores. The identification of a human Mad3/Bub1-related protein kinase, hBubR1, which can also bind Bub3 in mammalian cells, is described. Ectopically expressed hBubR1 also localizes to kinetochores during prometaphase, but only when hBub3 is overexpressed. We discuss the implications of the common interaction between Bub1 and hBubR1 with hBub3 for checkpoint control

A Novel Class of RanGTP Binding Proteins

The importin-α/β complex and the GTPase Ran mediate nuclear import of proteins with a classical nuclear localization signal. Although Ran has been implicated also in a variety of other processes, such as cell cycle progression, a direct function of Ran has so far only been demonstrated for importin-mediated nuclear import. We have now identified an entire class of ∼20 potential Ran targets that share a sequence motif related to the Ran-binding site of importin-β. We have confirmed specific RanGTP binding for some of them, namely for two novel factors, RanBP7 and RanBP8, for CAS, Pse1p, and Msn5p, and for the cell cycle regulator Cse1p from Saccharomyces cerevisiae. We have studied RanBP7 in more detail. Similar to importin-β, it prevents the activation of Ran's GTPase by RanGAP1 and inhibits nucleotide exchange on RanGTP. RanBP7 binds directly to nuclear pore complexes where it competes for binding sites with importin-β, transportin, and apparently also with the mediators of mRNA and U snRNA export. Furthermore, we provide evidence for a Ran-dependent transport cycle of RanBP7 and demonstrate that RanBP7 can cross the nuclear envelope rapidly and in both directions. On the basis of these results, we propose that RanBP7 might represent a nuclear transport factor that carries an as yet unknown cargo, which could apply as well for this entire class of related RanGTP-binding proteins

Cdc28 Activates Exit from Mitosis in Budding Yeast

The activity of the cyclin-dependent kinase 1 (Cdk1), Cdc28, inhibits the transition from anaphase to G1 in budding yeast. CDC28-T18V, Y19F (CDC28-VF), a mutant that lacks inhibitory phosphorylation sites, delays the exit from mitosis and is hypersensitive to perturbations that arrest cells in mitosis. Surprisingly, this behavior is not due to a lack of inhibitory phosphorylation or increased kinase activity, but reflects reduced activity of the anaphase-promoting complex (APC), a defect shared with other mutants that lower Cdc28/Clb activity in mitosis. CDC28-VF has reduced Cdc20- dependent APC activity in mitosis, but normal Hct1- dependent APC activity in the G1 phase of the cell cycle. The defect in Cdc20-dependent APC activity in CDC28-VF correlates with reduced association of Cdc20 with the APC. The defects of CDC28-VF suggest that Cdc28 activity is required to induce the metaphase to anaphase transition and initiate the transition from anaphase to G1 in budding yeast

The Elg1 Clamp Loader Plays a Role in Sister Chromatid Cohesion

Mutations in the ELG1 gene of yeast lead to genomic instability, manifested in high levels of genetic recombination, chromosome loss, and gross chromosomal rearrangements. Elg1 shows similarity to the large subunit of the Replication Factor C clamp loader, and forms a RFC-like (RLC) complex in conjunction with the 4 small RFC subunits. Two additional RLCs exist in yeast: in one of them the large subunit is Ctf18, and in the other, Rad24. Ctf18 has been characterized as the RLC that functions in sister chromatid cohesion. Here we present evidence that the Elg1 RLC (but not Rad24) also plays an important role in this process. A genetic screen identified the cohesin subunit Mcd1/Scc1 and its loader Scc2 as suppressors of the synthetic lethality between elg1 and ctf4. We describe genetic interactions between ELG1 and genes encoding cohesin subunits and their accessory proteins. We also show that defects in Elg1 lead to higher precocious sister chromatid separation, and that Ctf18 and Elg1 affect cohesion via a joint pathway. Finally, we localize both Ctf18 and Elg1 to chromatin and show that Elg1 plays a role in the recruitment of Ctf18. Our results suggest that Elg1, Ctf4, and Ctf18 may coordinate the relative movement of the replication fork with respect to the cohesin ring