DNA Damage & Repair

Research Summary

Determinants of DNA Replication Fidelity: process showing Pre-Replication, Replication and Post-Replication.

Mechanisms involved in DNA replication: pre-replication, replication and post-replication.

As its name implies, the DNA Replication Fidelity Group performs research aimed at understanding the DNA transactions that determine DNA replication fidelity. For example, several repair processes operate prior to DNA replication to remove the many types of DNA damage generated by endogenous cellular metabolism or exposure to the environment. These processes provide undamaged substrates for efficient and highly accurate DNA replication. High replication fidelity depends on the ability of DNA polymerases to select correct, rather than incorrect, nucleotides for incorporation into DNA without adding or deleting nucleotides. Polymerase selectivity is a prime determinant of fidelity at the replication fork and also during DNA synthesis associated with repair.

Exonucleolytic proofreading of mismatches can further increase DNA synthesis fidelity. When DNA damage is not repaired prior to replication, certain lesions can impede replication fork progression and reduce fidelity. For these circumstances, specialized translesion synthesis and repair processes maintain genome stability and improve cell survival. Finally, mismatches remaining in DNA are corrected by mismatch repair (MMR). MMR proteins also participate in signaling apoptosis following DNA damage, preventing mutagenic recombination, promoting meiotic recombination and modulating somatic hypermutation of immunoglobulin genes and the stability of misaligned repetitive DNA sequences.

The group is actively investigating many of these processes and how the environment perturbs them, thereby resulting in adverse effects on human health. For example, failure of the systems that determine replication fidelity can lead to mutations that underlie diseases such as cancer and hereditary neurodegenerative diseases. Accumulation of environmentally-induced DNA damage and mutations may contribute to aging. Structure-function studies of polymerases are relevant to the emergence of drug-resistant viruses and may be useful for drug design. Describing the functions of mismatch-repair proteins improves understanding of cellular responses to environmental stress and the efficacy of chemotherapeutic agents, the origins of certain forms of cancer, the emergence of antibiotic-resistant pathogenic bacterial and the development of normal germ cells. Finally, we study the incorporation of ribonucleotides into DNA during normal replication, the processes by which they are removed, and the evolutionary and mutagenic consequences of their presence and/or removal from DNA. Studies of mutations and putative functional polymorphisms in the genes encoding proteins participating in DNA replication fidelity processes are important for understanding individual variability in susceptibility to environmental diseases.

Major areas of research:

  • Polymerase selectivity and its role in DNA replication fidelity
  • Exonucleolytic proofreading
  • Replication infidelity and its role in disease and aging
  • Structure-function studies of replication proteins, especially DNA polymerases
  • Mechanisms of eukaryotic DNA mismatch repair
  • Mutations and polymorphisms in genes relevant to DNA replication fidelity
  • The incorporation of ribonucleotides into DNA during normal replication, the processes by which they are removed, and the evolutionary and mutagenic consequences of their presence and/or removal from DNA

Current projects:

  • Investigation of the functions of DNA polymerases, including their fidelity and the mechanisms by which errors are avoided and generated
  • Emphasis on error-prone polymerases in the Y family, DNA repair polymerases in the X family and replicative polymerases in the B family
  • The genetics and biochemistry of eukaryotic DNA mismatch repair

Thomas A. Kunkel, Ph.D., leads the DNA Replication Fidelity Group within the Genome Integrity and Structural Biology Laboratory. Kunkel has published numerous peer-reviewed articles in leading scientific journals, as well as several book chapters. He received his doctorate in 1977 from the University of Cincinnati. Following a postdoctoral fellowship at the University of Washington, he joined the NIEHS in 1982.

Video interview with Jessica Williams, Ph.D.