Duncan Clarke, PhD

Research Techniques:

Budding Yeast Genetics and Cell Biology, Cell Cycle Analysis, Sister Chromatid Cohesion Assays

Research Interests:

Yeast genetics and mammalian RNAi experiments are used to investigate
basic aspects of eukaryotic cell cycle control that are relevant for cancer
research.The Clarke lab is particularly interested in cell cycle checkpoint
controlsand in chromosome dynamics. Budding yeast is used as a model
organism,providing the most powerful genetic tools that are available
to researcherstoday. The validity of this approach, first realized by Nobel
Laureates Paul Nurseand Lee Hartwell, stems from the fact that yeast
and human cell cycle proteinsare remarkably well conserved evolutionarily.

Checkpoint Controls

Back in the early 1990s, the lab discovered a mammalian Topoisomerase
II-Dependent Checkpoint; a control mechanism that prevents the onset
of mitosis when chromosome condensation is not able to proceed normally.
More recently, the lab has identified a sub-pathway of the yeast DNA Replication
Checkpoint, a novel late S-phase signaling system that regulates the onset
of anaphase. This checkpoint maintains the cohesion between replicated sister
DNA molecules that is necessary to allow accurate chromosome segregation
during anaphase of mitosis. The nature of each of these intricate checkpoints
is a current area of focus.

At least in part, checkpoints control the stability of key cell cycle regulators such a
s the securin Pds1. Turn-over of the regulators is modulated by ubiquitin-dependent
proteolysis. Together with other researchers, we identified a novel ubiquitin-binding
domain called the UBA. Much work is needed to elucidate the molecular roles
of UBA domains in cell cycle processes and this is currently an extremely
exciting area of research.

Chromosome Dynamics

Cancer cells originate from normal cells that have acquired genome instability.
Accurate chromosome condensation and a high fidelity of chromosome segregation
are crucial to the maintenance of a stable genome. In addition to studying the cell
cycle checkpoints that monitor chromosome transmission, we are also interested
in the mechanics of condensation and segregation, processes that are not well
understood. A key goal is to define novel factors that organize the DNA molecules
within chromosomes undergoing dynamic changes throughout the cell cycle.

Selected Publications:

Bancant J & ClarkeDJ (2008) Kinetochore structure and spindle assembly checkpoint signaling in the budding yeast Saccharomyces cerevisiae. Frontiers in Bioscience 13:6787-6819

Diaz-Martinez LA, Gimenez-Alian JF and Clarke DJ (2008) Chromosome Cohesion: Rings, Knots, Orcs and Fellowship. J Cell Science 121:2107-2114.

Raveendranathan M, Chattopadhyay S, Bolon YT, Haworth J, Clarke DJ & Bielinsky AK (2006). Genome-Wide Replication Profiles of S Phase Checkpoint Mutants Reveal Fragile Sites in Yeast. EMBO J. in press

Andrews CA, Vas ACJ, Meier B, Giménez-Abián JF, Díaz-Martínez LA, VanderWaal K, Hsu W-S, Erickson S and Clarke DJ. A Mitotic Topoisomerase II Checkpoint in Budding Yeast is required for Genome Stability but acts independently of Pds1/Securin. Genes & Dev. In Press

Kang Y, Vossler R, Diaz-Martinez LA, Winter NS, Clarke DJ and Walters KJ (2006). UBL/UBA ubiquitin receptor proteins bind a common tetraubiquitin chain. J Mol Biol, 356(4):1027-1035.

Andrews CA, Giménez-Abián JF, Díaz-Martínez LA, Guacci V, Vas ACJ and Clarke DJ (2005). Evidence that the yeast spindle assembly checkpoint has a target other than the anaphase promoting complex. Cell Cycle, 4(11): 1553-1555.

Giménez-Abián JF, Díaz-Martínez LA, Waizenegger IC, Giménez-Martín G and Clarke DJ (2005). Separase is required at multiple pre-anaphase cell cycle stages in human cells. Cell Cycle, 4(11): 1574-1582.

Giménez-Abián JF, Díaz-Martínez LA, Wirth K, Andrews CA, Giménez-Martín G and Clarke DJ (2005). Regulated Separation of Sister Centromeres depends on the Spindle Assembly Checkpoint but not on the Anaphase Promoting Complex/Cyclosome. Cell Cycle, 4(11): 1559-1573.

Andrews CA & Clarke DJ (2005). MRX (Mre11/Rad50/Xrs2) mutants reveal dual intra-S-phase checkpoint systems in budding yeast. Cell Cycle 4:(8):1073-1077.

Clarke DJ, Segal M, Andrews CA, Rudyak SG, Jensen S, Smith K and Reed SI (2003). S-phase Checkpoint Controls Mitosis via an APC-independent Cdc20p Function. Nature Cell Biol 5(10): 928-935.

Clarke DJ, Segal M, Jensen S and Reed SI (2001). Mec1p regulates Pds1p levels in S-phase: Evidence for complex coordination of DNA replication with mitosis. Nature Cell Biol. 3:619-627.

Clarke DJ, Segal M, Mondésert G and Reed SI (1999). The Pds1 anaphase inhibitor and Mec1 kinase define distinct checkpoints coupling S phase with mitosis in budding yeast. Curr. Biol. 9:365-368.

Downes CS, Clarke DJ, Mullinger AM, Giménez-Abián JF, Creighton AM & Johnson RT (1994). A topoisomerase II-dependent G2 cycle checkpoint in mammalian cells. Nature 372:467-470.

To view these and other publications visit http://www.ncbi.nlm.nih.gov/PubMed
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