Cytokinesis mediated through the recruitment of cortexillins into the cleavage furrow

The fact that substrate-anchored Dictyostelium cells undergo cytokinesis in the absence of myosin II underscores the importance of other proteins in e nabling the cleavage furrow to constrict. Cortexillins, a pair of actin-bun dling proteins, are required for normal cleavage. They are targeted to the incipient furrow in wild-type and, more prominently, in myosin II-null cell s. No other F-actin bundling or cross-linking protein tested is co-localize d, Green fluorescent protein fusions show that the N-terminal actin-binding domain of cortexillin I is dispensable and the C-terminal region is suffic ient for translocation to the furrow and the rescue of cytokinesis. Cortexi llins are suggested to have a targeting signal for coupling to a myosin II- independent system that directs transport of membrane proteins to the cleav age furrow.