Active MPF, total active Cdc25, and Wee1 as a function of time. No DNA damage is assumed here, i.e., k4 = k10 = 0. Nuclear export of iCdc25Ps216/14–3–3 has the rate vex = kex[iCdc25Ps216/14–3–3] with kex = 1, and nuclear import of iCdc25 has the rate vin = 10−5. Each of the following parameters has the value 1.0: k1, k5, k7, k18, k9, k11, k13, k-8, k-9, k-23, k14′; each of the following is equal to 0.1: k8, k12, k22, k23, k20; each of the following is equal to 0.01: k6, k17, k2, k2′, k-2, k-7, k-18, k21; the following are set to zero: kPlk1, kPlk1′, kctak1, kctak1′, k8′, k9′, k-3′; k-1 = 10; k14 = 5 × 10−4; k15 = 10−2; k16 = 2 × 10−4; k3′ = 100; [totalChk1] = 1. Initial conditions: [Chk1P] = [iCdc25] = [aCdc25] = [preMPF] = 10−6; [MPF] = 10−8; [iCdc25Ps216] = 2 × 10−5; [Wee1] = 10−3; [iCdc25Ps216/14–3–3] = 0.03; [14–3–3] = 2; all other species are zero. All parameters and variables are dimensionless.