Description of Research Interests

Genome maintenance pathways are critical for faithful DNA replication, recombination, and repair, but they also have specialized functions in activated B cells where they participate in changing the sequence and structure of immunoglobulin genes. I take molecular, biochemical, and cellular approaches to investigate the function of highly conserved DNA repair processes. This research pays high dividends because it not only reveals basic mechanisms functioning to preserve genetic information but also key steps in the enzymology of adaptive immunity.

The broad goal of my research is to clarify the scope of DNA repair functions in the cell with a specific focus on the molecular mechanisms of immunoglobulin gene diversification. Immunoglobulin gene diversification is required for proper immunity and involves three mechanistically related pathways with distinct outcomes: somatic hypermutation, class switch recombination, and gene conversion. Somatic hypermutation produces base substitutions in the rearranged and expressed antibody variable regions, thereby altering antigen affinity. Class switch recombination is a regulated process of DNA deletion, which removes an expressed antibody constant region and rejoins the DNA within G-rich regions called “switch” regions, improving the efficacy of antigen clearance. Gene conversion uses upstream pseudogenes as templates for repair and is the primary mechanism of antibody variable-region diversity in some vertebrates. All three pathways are transcription coupled and depend on high levels of immunoglobulin gene expression and on the B cell-specific enzyme, activation induced deaminase (AID), which deaminates cytidine to produce uridine in single-stranded DNA. Mutagenic resolution of uridine in DNA is carried out by conserved DNA repair factors, but their precise roles are not yet defined.

Current research efforts launch from my recent findings demonstrating novel functions for two highly conserved DNA repair complexes. First, the DNA recombination and repair complex, MRE11/RAD50, has an abasic-lyase activity which functions in all three pathways of immunoglobulin gene diversification by producing DNA breaks in response to the sequential action of the AID and UNG proteins. Second, the mismatch repair heterodimer, MutSalpha, has a novel structure-binding activity that facilitates the joining of switch regions during class switch recombination. These results expand the known functions of essential repair factors and future research will investigate how they contribute both to the production high-affinity antibodies in B cells and to genome maintenance in all cell types.