RNG2P, A PROTEIN REQUIRED FOR CYTOKINESIS IN FISSION YEAST, IS A COMPONENT OF THE ACTOMYOSIN RING AND THE SPINDLE POLE BODY

Background: An actomyosin-based contractile ring plays a pivotal role in cytokinesis. Despite the identification of many components of the r ing, the steps involved in its assembly are unknown. The fission yeast Schizosaccharomyces pombe is an attractive organism in which to study cytokinesis because its cell cycle has been well characterized; it di vides by medial fission using an actomyosin ring; and a number of S. p ombe mutants defective in actomyosin ring assembly have been isolated. Here, we have characterized one such mutant, rng2. Results: Temperatu re-sensitive rng2 mutants accumulated F-actin cables in the medial reg ion of the cell but failed to organize the cables into a ring. In mg2- null mutants, only a spot-like structure containing F-actin was detect ed. The mg2(+) gene encodes a protein related to human IQGAP1,a protei n that binds actin and calmodulin and is a potential effector for the Rho family of GTPases. Rng2p localized to the actomyosin ring and to t he spindle pole body (SPB) of interphase and mitotic cells. Localizati on of Rng2p to the actomyosin ring but not the SPB required F-actin. R ng2p interacted with calmodulin, a component of the SPB and the actomy osin ring. The rng2 gene showed genetic interactions with three other actomyosin ring assembly mutants, cdc4, cdc12, and mg5. Conclusions: T he S. pombe IQGAP-related protein Rng2p is a component oi the actomyos in ring and the SPB and is required for actomyosin ring construction f ollowing assembly of F-actin at the division site. (C) Current Biology Ltd ISSN 0960-9822.