Models of septin complex reorganization. (a) Yeast septins form an octameric complex. The four transition dipole moments of a paired complex average to an overall anisotropy value (arrows). A collar of septin filaments parallel to the mother–bud axis is split into two rings with filaments perpendicular to the mother–bud axis. (b) Septin filaments on opposing sides of the division plane rotate against one another, canceling the overall polarization until, when the process is completed, a perpendicular polarization reemerges. (c) A majority of filaments are oriented parallel to the mother–bud axis while there are also perpendicular filaments. The reorientation represents a shift in equilibrium between the two arrangements. (d) The septin filaments completely disassemble and later reassemble in perpendicular orientation while remaining confined to the bud neck.