Randy Legerski, Ph.D.

The overall objective of my laboratory is the study of molecular mechanisms of cellular responses to DNA damage in mammalian systems. We are particularly interested in the relationship between these pathways and the degenerative processes of carcinogenesis and aging in humans. Our current focus is on the mechanisms of repair of interstrand cross-links in DNA. Repair of interstrand cross-links is a significant topic for human health since important chemotherapeutic agents used against cancer and other diseases can induce these lesions. In addition, food sources and mammalian metabolism can produce cross-linking agents that lead to DNA damage and genomic instability in cells. Genetic studies, primarily in yeast, have shown that homologous recombination is a primary pathway of cross-link repair; however, the early steps of damage recognition and processing of these lesions are still undefined. To investigate these pathways, we have developed a mammalian cell-free biochemical assay that has allowed us to begin identifying factors involved in this pathway and to elucidate the repair mechanisms. Using this in vitro assay, we have purified several factors involved in the initial stages of cross-link repair, and their characterization is currently a major focus of the laboratory. Our long-term goal is to completely reconstitute the mammalian interstrand cross-link repair pathway.

In addition to our biochemical studies, we are also focusing on the characterization of a small mammalian gene family whose homologue in yeast is specifically involved in cross-link repair. The snm1 (sensitivity to nitrogen mustard) mutant of Saccharomyces cerevisiae was first identified in a screen for strains sensitive to bifunctional alkylating agents. We have identified 3 mammalian homologues of this gene, SNM1, SNM1B, and Artemis, and are currently characterizing their functions in mammalian cells. In constrast to the role scSNM1 we have found that SNM1 and Artemis are involved in mediating cell cycle checkpoints in mammalian cells in response to both DNA damage and mitotic stress. We are continuing to use biochemical, molecular biological, and genetic approaches, including gene-targeting strategies in the mouse, to elucidate the function of the mammalian SNM1 genes.

Recent publications

Ahkter, S., Richie, C.T., Zhang, N., Behringer, R.R., Zhu, C., and Legerski, R.J. (2005) Snm1-Deficient Mice Exhibit Accelerated Tumorigenesis and Susceptibility to Infection. Molec. Cell. Biol. 25, 10071-10078.
Zhang, N., Kaur, R., Lu, X., Shen, X., Li, L., and Legerski, R.J. (2005) The Pso4 mRNA Splicing and DNA Repair Complex Interacts with WRN for Processing of DNA Interstrand Cross-Links. J. Biol. Chem. 280, 40559-40567.
Zhang, X., Succi, J., Feng, Z., Prithivirajsingh, S., Story, M.D., and Legerski, R.J. (2004) Artemis Is a Phosphorylation Target of ATM and ATR and Is Involved in the G2/M DNA Damage Checkpoint Response. Molec. Cell. Biol., 24, 9207–9220.
Zheng, H., Wang, X., Warren, A.J., Legerski, R.J., Nairn, R.S., Hamilton, J.W., and Li, L. (2003) Nucleotide Excision Repair- and Polymerase η-Mediated Error-Prone Removal of Mitomycin C Interstrand Cross-Links. Molec. Cell. Biol. 23, 754–761.
Richie, C.T., Peterson, C.A., Lu, T., Hittelman, W.N., Carpenter, P.B., and Legerski, R.J. (2002) hSnm1 Colocalizes and Physically Associates with 53BP1 Before and After DNA Damage. Molec. Cell. Biol. 22, 8635–8647.
Zhang, N., Lu, X., Zhang, X., Peterson, C.A., and Legerski, R.J. (2002) hMutSb is Required for the Recognition and Uncoupling of Psoralen Interstrand Cross-links in Vitro. Molec. Cell. Biol. 22, 2388–2397.

Zhang, X., Richie, C., and Legerski, R.J. (2002) Translation of hSNM1 is Mediated by an Internal Ribosome Entry Site that Upregulates Expression during Mitosis. DNA Repair 1, 379–390.
Wang X, Peterson CA, Zheng H, Nairn RS, Legerski RJ, Li L (2001) Involvement of nucleotide excision repair in a recombination-independent and error-prone pathway of DNA interstrand cross-link repair. Mol Cell Biol 21, 713–720.
Li L, Peterson CA, Lu X, Wei P, Legerski RJ (1999) Interstrand cross-links induce DNA synthesis in damaged and undamaged plasmids in mammalian cell extracts. Mol Cell Biol 19, 5619–5630.
Pan Z-Q, Reardon JT, Li L, Flores-Rozas H, Legerski RJ, et al. (1995) Inhibition of nucleotide excision repair by the cyclin-dependent kinase inhibitor p21. J Biol Chem 270, 22008–22016.
Li L, Lu X, Peterson CA, Legerski RJ (1995) An interaction between DNA repair factor XPA and replication protein A (RPA) appears essential for nucleotide excision repair. Mol Cell Biol 15, 5396–5402.
Tebbs RS, Zhao Y, Tucker JD, Scheerer JB, Siciliano MJ, Hwang M, Lin N, Legerski RJ, et al. (1995) Correction of chromosomal instability and sensitivity to diverse mutagens by a cloned cDNA of the XRCC3 DNA repair gene. Proc Natl Acad Sci USA 92, 6354–6358.
Henning KA, Peterson CA, Legerski RJ, Friedberg EC (1994) Cloning the Drosophila homolog of the xeroderma pigmentosum complementation group C gene reveals homology between the predicted human and Drosophila polypeptides and that encoded by the yeast RAD4 gene. Nucleic Acids Res 22, 257–261.
Li L, Bales ES, Peterson CA, Legerski RJ (1993) Characterization of molecular defects in xeroderma pigmentosum group C. Nat Genet 5, 413–417.
Legerski RJ, Peterson C (1992) Expression cloning of a human DNA repair gene involved in xeroderma pigmentosum group C. Nature 359, 70–73.