In vitro Reactivation of the Contractile Ring in the Fission Yeast Cell-ghost

Cytokinesis in many eukaryotes involves the closure of an actomyosin-based contractile ring (CR). We have established an in vitro system to study CR contraction. We show that CRs of permeabilized fission yeast cells undergo rapid contraction in an ATP and myosin-II-dependent manner in the absence of other cytoplasmic constituents. Neither actin polymerization nor its disassembly was required for closure of CRs although addition of exogenous actin cross-linking proteins blocked ring contraction. Using CRs generated from fission yeast cytokinesis mutants, we show that not all proteins required for assembly of the CR are required for its contraction in vitro.