Spinning septins

Septin filaments in yeast do a right-angled turn in the middle of cell division, according to Alina Vrabioiu and Tim Mitchison (Harvard Medical School, Boston, MA). The filaments initially align parallel to the spindle axis but then rotate 90° to form two circumferential rings that flank the cytokinetic furrow.

Septin filaments help cells divide, but just how they do so has remained mysterious. The direction of septin-dependent striations varied between experiments, plus the striations may have been a pattern set up by proteins that bind septins, not the septins themselves.

Now, the Boston team has directly monitored the direction of septin filaments. They attached a green fluorescent protein (GFP) to septin by linking together two rigid α-helices. Polymerizing the septin–GFP molecules in a filament lined up all the GFPs. Polarized light would...