The goal of my research is to understand how the protein MRE11 contributes to Ig gene diversification. MRE11 is a member of the multifunctional MRE11/RAD50/NBS1 (MRN) complex, which is critical both to Ig gene diversification and other pathways of DNA repair. A heterotetramer of MRE11/RAD50 (MR) forms the core of this complex, while NBS1 serves as the regulatory subunit, and governs nuclear localization and catalytic efficiency. RAD50 is an elongated protein related to the SMC (structural maintenance of chromosome) protein family, and may tether DNA ends during repair.
MRE11 was first identified as a 3'-5' exonuclease and endonuclease, and subsequently shown by the Maizels laboratory to function as an AP lyase. In Ig gene diversification, the exonuclease activity is thought to promote double-strand break repair in class switch recombination, and the AP lyase is thought to cleave DNA at abasic (AP) sites generated when Uracil DNA Glycolsylase (UNG) removes uracil generated by AID.
The members of the MRN complex are essential in vertebrate cells, making it difficult to study function by targeted deletion. To overcome this, my plan is to identify active site mutations that separate the enzymatic activities of MRE11, and then to determine the biological functions using these separation of function alleles.
