Filament-forming cytoskeletal GTPase. Required for normal organization of the actin cytoskeleton. Required for normal progress through mitosis. Involved in cytokinesis. Required for normal association of CENPE with the kinetochore. Plays a role in ciliogenesis and collective cell movements. Forms a filamentous structure with SEPTIN12, SEPTIN6, SEPTIN2 and probably SEPTIN4 at the sperm annulus which is required for the structural integrity and motility of the sperm tail during postmeiotic differentiation (By similarity). Septins polymerize into heterooligomeric protein complexes that form filaments, and associate with cellular membranes, actin filaments and microtubules. GTPase activity is required for filament formation. Filaments are assembled from asymmetrical heterotrimers, composed of SEPTIN2, SEPTIN6 and SEPTIN7 that associate head-to-head to form a hexameric unit. Within the trimer, directly interacts with SEPTIN6, while interaction with SEPTIN2 seems indirect. In the absence of SEPTIN6, forms homodimers. Interacts directly with CENPE and links CENPE to septin filaments composed of SEPTIN2, SEPTIN6 and SEPTIN7. Interacts with SEPTIN5, SEPTIN8, SEPTIN9 and SEPTIN11. Component of a septin core octomeric complex consisting of SEPTIN12, SEPTIN7, SEPTIN6 and SEPTIN2 or SEPTIN4 in the order 12-7-6-2-2-6-7-12 or 12-7-6-4-4-6-7-12 and located in the sperm annulus; the SEPTIN12:SEPTIN7 association is mediated by the respective GTP-binding domains (By similarity). Distributed throughout the cytoplasm in prometaphase cells. Associated with the spindle during metaphase. Associated with the central spindle and at the cleavage furrow in anaphase cells. Detected at the midbody in telophase. Associated with actin stress fibers. Found in the sperm annulus (By similarity). Coordinated expression with SEPTIN2 and SEPTIN6. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family. Truncated N-terminus.