ANILLIN, A CONTRACTILE RING PROTEIN THAT CYCLES FROM THE NUCLEUS TO THE CELL CORTEX

We report the cDNA sequence and localization of a protein first identi fied by actin filament chromatography of Drosophila embryo extracts as ABP8 (Miller, K. G., C. M. Field, and B. M. Alberts. 1989. J. Cell Bi ol. 109:2963-2975). The cDNA encodes a 1201-amino acid protein which w e name anillin. Anillin migrates at 190 kD on SDS-PAGE. Anillin is exp ressed throughout Drosophila development and in tissue culture cells. By immunofluorescence, anillin localizes to the nucleus of interphase cells, except in the syncytial embryo where it is always cytoplasmic. During metaphase, it is present in the cytoplasm and cortex, and durin g anaphase-telophase it becomes highly enriched in the cleavage furrow along with myosin II. In the syncytial embryo, anillin, along with my osin-II, is enriched in cortical areas undergoing cell cycle regulated invagination including metaphase furrows and the cellularization fron t. In contractile rings, metaphase furrows, and nascent ring canals, a nillin remains bound to the invaginated cortex suggesting a stabilizin g role. Anillin is not expressed in cells that have left the cell cycl e. Anillin isolated from embryo extracts binds directly to actin filam ents. The domain responsible for this binding has been mapped to a reg ion of 244 amino acids by expression of protein fragments in bacteria. This domain, which is monomeric in solution, also bundles actin filam ents. We speculate that anillin plays a role in organizing and/or stab ilizing the cleavage furrow and other cell cycle regulated, contractil e domains of the actin cytoskeleton.