FIGURE 1.

Protein structure, intracellular localization, and putative function of KCHs. (A) Representative domain structure of KCHs. The N-terminal CH domain (red) is necessary but not sufficient for actin binding. The motor domain (green) contains the ATP and MT binding sites. It is situated between coiled-coil domains, which facilitate dimerization. (B) Schematic of two possible conformations of the KCH dimer with the MT- and AF-binding sites being freely accessible: a flexible dimeric stalk (left) and a stiffer tetrameric stalk configuration (right). (C) Intracellular localization of KCHs at the cell cortex (left) and in the cell midplane (right) of an idealized BY2 cell during interphase. (D) Two alternative working models of KCH functioning in pre-mitotic nuclear positioning: “Sliding model” (left) and “Pushing/pulling model” (right). The cortical cytoskeleton is depicted as dashed red-green frame. The small green arrows represent forces transmitted via MTs. The large green arrows represents the direction of the resulting net force. The red arrows (labeled with a question mark) indicate a speculative mechanism of force transmission via AFs. (E) One putative function of KCHs may be to transport AFs relative to MTs toward the minus-end.