GTP binding is required for SEPT12 to form filaments and to interact with SEPT11.

Septins are a family of filament-forming GTP-binding proteins involved in a variety of cellular process such as cytokinesis, exocytosis, and membrane dynamics. Here we report the biochemical and immunocytochemical characterization of a recently identified mammalian septin, SEPT12. SEPT12 binds GTP in vitro, and a mutation (Gly56 to Asn) in the GTP-binding motif abolished binding. Immunocytochemical analysis revealed that wild-type SEPT12 formed filamentous structures when transiently expressed in Hela cells whereas SEPT12G56A generated large aggregates. In addition, wild-type SEPT12 failed to form filaments when coexpressed with SEPT12G56A. We also observed that GTP-binding by SEPT12 is required for interaction with SEPT11 but not with itself.