Kerscher Lab Home Page

Welcome to the Kerscher lab

     at the Biology Department of the College of William & Mary, VA.

RESEARCH BACKGROUND:

The Role of SUMO in Chromosome Segregation and Genome Integrity

The Paramount Importance of a Tightly Controlled Chromosome Cycle:

The chromosome cycle defines the controlled duplication, packaging and faithful segregation of an organism’s genetic material from one cell to the next. In humans, the consequences of faulty chromosome segregation and the inability to repair DNA damage have been implicated in cancer, aging and congenital birth defects. Many proteins that can affect the chromosome cycle have been identified and studied using budding yeast, a eukaryotic model organism (see figure) . These yeast proteins often have orthologs in multicellular eukaryotes including humans. My research involves the study of proteins that ensure an efficient chromosome cycle (Ref. 4,5,6), and I focus on the role that a small protein modifier, SUMO, plays in chromosome segregation and genome integrity (Ref. 1,2,3). My research plan is particularly well suited for undergraduate research because it combines the tangible and easily mastered budding yeast model organism with a relevant and exciting biological question:

How do Targets and Components of the Sumoylation Machinery Affect the Chromosome Cycle? SUMO, a ubiquitin-like protein, can become covalently attached to specific protein targets. Unlike Ubiquitin, SUMO attachment does not target proteins for degradation, but appears to modulate functional properties like localization, activation, interactions and half-life (1,2). Among the targets of SUMO attachment are proteins that play important roles in the chromosome cycle including the topisomerase Top1 and the DNA helicase Srs2. Regulation of SUMO modification on these proteins is mediated by SUMO ligases and proteases. SUMO ligases, three of which have been identified in yeast to date, ascertain that the right targets are modified with SUMO during the process of SUMO modification. SUMO proteases of the Ulp1 family clip SUMO off the target proteins. Studies with conditional mutants of SUMO and the SUMO protease Ulp1 (see figure below) indicate that SUMO addition and removal is important for mitosis. A temperature sensitive ulp1 mutant (ulp1ts -- Li S.J., Hochstrasser M. (1999)) accumulates high levels of sumoylated proteins, DNA repair intermediates and arrests in mitosis. My work focuses on proteins that interact with Ulp1 in order to understand how SUMO dynamics affect the cell division cycle.

We have recently identified a novel interactor with Ulp1, Hex3.  Hex3 is part of a complex with Slx8 and both proteins are involved in genome integrity and the DNA damage response (Ref. 1).  Together, the Hex3/Slx8 complex constitutes a Ubiquitin ligase and ubiquitinates purified Rad52, a protein involved in recombination and DNA repair.  Our lab is actively looking for (and testing) additional Hex3/Slx8 substrates.  Additionally, we have identified a human protein that can take over the function of Hex3/Slx8 in yeast cells.  Since Hex3/Slx8 are involved in genome maintenance we hypothesize that this protein plays similar function in human cells.

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Figure: YEAST CELLS & NUCLEI: The Ulp1 SUMO protease localizes to the nuclear periphery of yeast cells. Shown are two

yeast cells expressing the GFP tagged Ulp1 protein. The image on the left was taken using a fluorescent microscope.

An inverted image delineating the cell and nuclear outline is shown on the right. Cell diameter is about 5µm.

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TOOL TIME:

YES IT'S STILL POSSIBLE Your microscope run by a Mac and OS X:

Epi-fluorescent microscopy + Image collection using an ALL-Mac-OS X set-up

We have converted our microscope set-up to a cooled qimaging Retiga-SRV firewire camera and Biovision software (formerly IPlab) on a Zeiss Axioskop II microscope. The computer running our software, firewire Qcam and shutter is a white 20 inch apple imac with Intel processor. No bootcamp or other tricks needed -- the software and camera run native on OSX (Note: We are still evaluating if the software can run on leopard). I will soon post additional hardware and software specs and some company phone numbers here. Until then feel free to email.

Selected References:

1) Yang Xie* , Oliver Kerscher* , Mary B. Kroetz , Heather F. McConchie , Patrick Sung , Mark Hochstrasser. (2007) The yeast HEX3-SLX8 heterodimer is a ubiquitin ligase stimulated by substrate sumoylation. J. Biol Chem. 23(47)34176-34184* denotes joint first authors

2) Kerscher O. (2007) SUMO junction-what's your function? New insights through SUMO-interacting motifs. EMBO Reports 8(6): 550-555

3) Kerscher, O., Felberbaum, R. and Hochstrasser, M. (2006) Modification of proteins by ubiquitin and ubiquitin-like proteins. Annu Rev Cell Dev Biol, 22, 159-180.

4) Kerscher, O., Crotti L.B. & Basrai, M.A. Recognizing Chromosomes in Trouble: Association of the Spindle Checkpoint Protein Bub3p with Altered Kinetochores and a Unique Defective Centromere. Mol. Cell Biol. 23:6406-6418 (2003)

5) Iouk, T.*, Kerscher, O.*, Scott, R. J., Basrai, M. A. & Wozniak, R. W. The yeast nuclear pore complex
functionally interacts with components of the spindle assembly checkpoint. J. Cell Biol. 159:807-819
(2002) * denotes joint first authors

6) Kerscher, O., Hieter, P., Winey, M. & Basrai, M.A. Novel role for a Saccharomyces cerevisiae
nucleoporin, NUP170, in chromosome segregation. Genetics. 157:1543-1553 (2001)

Education & Positions:

• Assistant Professor, Biology, The College of William & Mary, Williamsburg, VA, 2006-present

• Postdoctoral Staff Associate, Hochstrasser Lab, Yale University, New Haven, CT, 2003-2006

• CRTA Fellow, Basrai Lab, The National Cancer Institute, Bethesda, MD, 1999-2003

• Ph.D., Jensen Lab, The Johns Hopkins School of Medicine, BCMB program, Baltimore, MD, 1999

• M.A. in Biotechnology, The Johns Hopkins University, Baltimore, MD, 1995

• B.A. in Biology, The Johns Hopkins University, Baltimore, MD, 1992

• University of Cologne, Biology, Germany, 1987-1988

last updated February 28, 2008 -- all images created by OK