small GTPase-mediated signal transduction septation initiation signaling septation initiation signalling septation initiation network septation initiation signaling cascade The series of molecular signals, mediated by the small GTPase Ras, that results in the initiation of contraction of the contractile ring, at the beginning of cytokinesis and cell division by septum formation. The pathway coordinates chromosome segregation with mitotic exit and cytokinesis. GO:0031028 biological_process SIN