Biosciences Graduate Program

Todd Washington, PhD


Associate Professor of Biochemistry
Associate Professor of Radiation Oncology

Contact Information

Primary Office: 4-610 BSB
Iowa City, IA 52242
Primary Office Phone: 319-335-7518

Web: Washington Laboratory


BA, Philosophy, The Ohio State University
BS, Biology, The Ohio State University
PhD, Biochemistry, The Ohio State University

Post Doctoral, University of Texas Medical Branch at Galveston

Education/Training Program Affiliations

Biosciences Graduate Program
Department of Biochemistry PhD
Interdisciplinary Graduate Program in Molecular and Cellular Biology
Interdisciplinary Graduate Program in Translational Biomedicine
Medical Scientist Training Program

Research Summary

Classical, replicative DNA polymerases synthesize DNA in a template-dependent fashion with remarkable efficiency and fidelity. They achieve rates as high as 1,000 nucleotide incorporations per second with error frequencies as low as one error per one million nucleotides incorporated. What these amazing enzymes cannot do, however, is replicate through DNA lesions that arise spontaneously or are formed upon attack by a plethora of DNA damaging agents including oxygen free radicals and radiation. Consequently, organisms have evolved specialized polymerases to replicate through lesions. DNA polymerase eta is one such specialized polymerase. Inactivation of DNA polymerase eta in yeast leads to an increase in the frequency of ultraviolet (UV) radiation-induced mutations. This indicates that the replication of UV- induced lesions by this polymerase is error-free ( i.e. , not mutagenic). In vitro , DNA polymerase eta has the unprecedented ability to accurately replicate through a thymine dimer, a common UV-induced lesion. Furthermore, defects in human DNA polymerase eta are responsible for the cancer prone genetic disorder, the variant form of xeroderma pigmentosum. DNA polymerase zeta is another specialized polymerase. Inactivation of DNA polymerase zeta in yeast leads to a dramatic decrease in the frequency of mutations induced by a wide range of DNA damaging agents. This indicates that the replication of numerous lesions by this polymerase is mutagenic. In vitro , DNA polymerase zeta has the remarkable ability to efficiently extend from primer- terminal mismatches containing template lesions. Thus, DNA polymerase zeta likely functions in the mutagenic replication of damaged DNA by extending from nucleotides inserted opposite lesions by other polymerases?often the classical, replicative polymerases themselves. Our long- term goal is to understand the mechanisms of DNA polymerases involved in both mutagenic and error-free replication of DNA damage at the thermodynamic, kinetic, and structural level. We use a variety of approaches including equilibrium binding techniques, transient state kinetic analyses (both rapid chemical quench flow and fluorescence-based stopped flow methods), and the characterization of mutant proteins generated by site-directed mutagenesis. We hope that this work will contribute to our understanding of the origins of mutations and cancers and perhaps gain new insights into their prevention.

Center, Program and Institute Affiliations

Holden Comprehensive Cancer Center

Selected Publications

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Pryor J, Washington M.  Pre-steady state kinetic studies show that an abasic site is a cognate lesion for the yeast Rev1 protein.  DNA repair.  2011 November. 10(11):1138-44.

Freudenthal B, Brogie J, Gakhar L, Kondratick C, Washington M.  Crystal structure of SUMO-modified proliferating cell nuclear antigen.  Journal of molecular biology.  2011 February. 406(1):9-17.

Washington M, Carlson K, Freudenthal B, Pryor J.  Variations on a theme: eukaryotic Y-family DNA polymerases.  Biochimica et biophysica acta.  2010 May. 1804(5):1113-23.

Freudenthal B, Gakhar L, Ramaswamy S, Washington M.  Structure of monoubiquitinated PCNA and implications for translesion synthesis and DNA polymerase exchange.  Nature structural & molecular biology.  2010 April. 17(4):479-84.

Freudenthal B, Gakhar L, Ramaswamy S, Washington M.  A charged residue at the subunit interface of PCNA promotes trimer formation by destabilizing alternate subunit interactions.  Acta crystallographica. Section D, Biological crystallography.  2009 June. 65(Pt 6):560-6.

Freudenthal B, Ramaswamy S, Hingorani M, Washington M.  Structure of a mutant form of proliferating cell nuclear antigen that blocks translesion DNA synthesis.  Biochemistry.  2008 December. 47(50):13354-61.

Howell C, Kondratick C, Washington M.  Substitution of a residue contacting the triphosphate moiety of the incoming nucleotide increases the fidelity of yeast DNA polymerase zeta.  Nucleic acids research.  2008 March. 36(5):1731-40.

Howell C, Prakash S, Washington M.  Pre-steady-state kinetic studies of protein-template-directed nucleotide incorporation by the yeast Rev1 protein.  Biochemistry.  2007 November. 46(46):13451-9.

Carlson K, Johnson R, Prakash L, Prakash S, Washington M.  Human DNA polymerase kappa forms nonproductive complexes with matched primer termini but not with mismatched primer termini.  Proceedings of the National Academy of Sciences of the United States of America.  2006 October. 103(43):15776-81.

Date Last Modified: 02/20/2015 - 14:41:10