Domain organization of Dictyostelium MHCKs. All three enzymes contain a strongly conserved seven-fold WD repeat domain at the carboxyl-terminus. MHCK-A has a unique amino-terminal domain of ~ 500 residues that forms a coiled-coil domain responsible for oligomerization and for localization to anterior actin-rich cell extensions. MHCK-B has an amino-terminal segment of ~ 115 residues of currently unknown function. GFP was fused at the amino-terminus of each MHCK for the studies presented here (at codon 2 in each case). "CAT" indicates position of the conserved protein kinase catalytic domain in each enzyme. "SNPQ" (black boxes) indicates position of segments of MHCK-B and MHCK-C that display low amino acid complexity and are rich in serine, asparagine, proline, and glutamine residues.