Academic Background

Ph. D. (1977) Rutgers University

DNA Repair and Damage Prevention Genes

DNA repair and damage prevention genes function to maintain the integrity of the genome by preventing mutagenesis and lethality in response to DNA damage produced by endogenous and exogenous agents.  The repair genes act, either by repairing damaged bases, restoring them to their undamaged state, or by removing damaged bases from DNA and replacing them.  The protection genes function either by detoxifying mutagenic DNA damaging agents, or by protecting DNA from interaction with such agents.  DNA repair deficiencies in humans result in an increased incidence of cancer in affected individuals, underscoring the importance of developing a thorough understanding of human DNA repair and protection genes and their mechanisms of action.

Identification and characterization of human oxidative repair and protection genes.  We are using functional genomics to identify human DNA repair genes.  The basic methods we use are to introduce and express human cDNAs in E. coli mutants defective in repair of oxidative DNA damage.  The inability of these E. coli mutants to repair oxidative DNA damage causes a mutator phenotype that results from spontaneous oxidative DNA damage.  Expression of human DNA repair genes, or genes that prevent oxidative DNA damage complement the mutator phenotype and are easily identified by their colony phenotype.  The genes identified by these procedures are then analyzed using biochemical and genetic approaches.  The methods include the use of bacterial, yeast and mammalian genetics and molecular biology techniques in order to determine the activities of the gene products, their DNA sequences, and the biochemical processes that allow interspecies phenotypic complementation to occur.

Our initial searches resulted in the identification of the human OXR1 and PC4 genes as two genes that protect eukaryotes from oxidative mutagenesis.  These two genes are able to complement repair deficient mutants ofE. coli and suppress the mutator phenotype.  We have made mutants of yeast genes homologous to OXR1 and PC4 and demonstrated that these mutants are sensitive to treatments with the oxidative agent hydrogen peroxide.  We are now in the process of determining the mechanisms by which these genes protect cells from the consequences of oxidative damage and are examining their roles in oxidation protection in mammalian cells.  We are also continuing to search for more human genes that are able to complement the mutator phenotype of the oxidation sensitive strains of E. coli in order to expand our collection of this class of genes.

OXR1 localizes to mitochondria and is induced in response to oxidative stress in yeast and in human cells.  Mitochondria produce reactive oxygen species as a by-product of energy production, thus localization of gene products that protect cells from oxidative damage may be related to its cellular function and current research efforts focus on this aspect of OXR1.

PC4 interacts with the human XPG protein in vitro, causing its displacement from DNA.  XPG is a key player in several types of DNA repair.  Our results suggest that PC4 functions in an XPG-dependent pathway of DNA repair specific for oxidative DNA damage and our current research focuses on this possibility.