Electron micrographs of rotary shadowed replicas of alpha-Ca2+/calmodulin-dependent protein kinase II reveal a flower-shaped multimeric molecule with a central particle surrounded by 8-10 smaller peripheral particles. Peripheral particles are attached to the central particle by thin arms or "linkers." Movement of peripheral particles to contact each other for autophosphorylation is likely to involve these linkers. It has generally been accepted that the segment 317-328 of the alpha-subunit constitutes the linker domain. In the present study we test this assumption by generating a mutant lacking the proposed sequence. The mutant has biochemical and morphological properties similar to those of the wild type, and a thin linker is occasionally observed in replicas from either type. The results indicate that the deleted sequence does not correspond to the linker domain. This conclusion, combined with observations from two recent studies which identify the C-terminal domain involved in oligomerization, narrows down the location of the linker domain within the sequence 330-354.