Required for the assembly and the contraction of the actomyosin ring at the bud neck during cytokinesis. Seems to be involved in additional tasks during cell division like axial bud-site selection and targeted secretion by recruiting the spatial landmark BUD4, the septin CDC12 and the secretion landmark SEC3 to the bud neck. May be regulated by calcium ions. Interacts with AFR1, AKR1, activated CDC42, calmodulin (CMD1), myosin MYO1 and its light chain MLC1, BUD4, INN1, SEC3 and TEM1. Forms a ring at the bud neck in a MLC1-dependent manner, which contracts at the end of cytokinesis. The calponin homology (CH) domain binds to actin filaments and is required for their recruitment to the bud neck. The IQ domains provide the interaction surface for the myosin light chain MLC1. The Ras-GAP domain is required for contraction of the actomyosin ring and is needed for the interaction with TEM1. It probably does not stimulate GTPase activity. Present with 279 molecules/cell in log phase SD medium.