Modulation of septin higher-order structure by the Cdc28 protein kinase

Septins are a family of eukaryotic guanosine phosphate-binding proteins that form linear heterooligomeric complexes, which, in turn, polymerize end-on-end into filaments. These filaments further assemble into higher-order structures at distinct subcellular locations. Dynamic changes in the organization of septin cortex structures appear during cell cycle progression. A variety of regulatory proteins and posttranslational modifications are involved in changes to the structure of septin assemblies during the entire cell cycle. In particular, septin-associated protein kinases mediate changes to septin higher order structures or interconnect cellular morphogenesis with the cell cycle. Yeast cyclin-dependent kinase, a master cell cycle regulator, is required for the initiation of a new septin ring. Here, using epifluoresence and electron microscopy, we show that upon phosphorylation by the Cdc28 kinase, septin filaments disassemble into hetero-octameric building blocks, and that filament depolymerization is specifically G1 cyclin-dependent.