Septin ring component required for cytokinesis; septins are GTP-binding proteins that assemble into rod-like hetero-oligomers that associate to form rod shaped protofilaments that polymerize end-to-end forming filaments; mother-bud neck localized septin rings act as scaffolds for recruiting cell division factors and as barriers to prevent diffusion of specific proteins between mother and daughter cells; C-terminal amphipathic helix senses membrane curvature tuned by oligomerization