To determine the stoichiometry of GINS in the CMG-Mcm10 complex, a Flag purification of CMG-Mcm10 was analyzed in a 10% PAGE gel followed by densitometric analysis. The result indicates the following stoichiometry: 1.0 Mcm2-7, 1.2 Mcm10, 0.87 Sld5, and 2.6 Psf1 + Psf2 (they co-migrate for an average of 1.3 each). The Psf3 runs at the dye front and could not be quantitated. FLAG columns capture some free Cdc45 and thus overestimate the Cdc45-FLAG subunit; MonoQ analysis removes free Cdc45 (see Figure 2—figure supplement 4).