This is the N-terminal forkhead-associated (FHA) domain found in Drosophila mutator 2 (MU2) protein. FHA domains are generally phosphothreonine (pThr) specific-binding domains and are present in DNA repair and checkpoint proteins. However, phosphothreonine binding is not conserved in the MU2 active site pocket due to the absence of three key residues needed for pThr binding. Dimerization, is conserved between FHA domains of Drosophila MU2 and human MDC1 albeit through different interfaces. The MU2 FHA domain dimerizes via the beta-sheet 2, the MDC1 FHA domain dimerizes via the opposite beta-sheet 1 [1].

1: Dimerization, but not phosphothreonine binding, is conserved between the forkhead-associated domains of Drosophila MU2 and human MDC1. Luo S, Ye K; FEBS Lett. 2012;586:344-349. PMID:22273583