By sequence analysis we show that the U104 domain found in the UNC104 subfamily of kinesins is a forkhead homology-associated domain (FHA). A combination of limited proteolysis, mass spectroscopy, and physicochemical analysis define this domain as a genuine autonomously folding domain. Our data show that the FHA domain is shorter than previously reported since the C-terminal α-helix is not part of its minimum core. Key amino acids postulated to recognize phosphorylated residues are conserved. These data suggest that the kinesin FHA domains are functional domains involved in protein–protein interactions regulated by phosphorylation.
