Cys → Ser changes in the _E, β, and γ subunits: Negative and neutral effects on the secretion of Fib₄₂₀. Cys → Ser changes were made in the fibrinogen subunits at the positions indicated above the lanes. COS cells were transfected with pED4-vectors containing _E, β, and γ (either wild-type or mutant) cDNAs as shown; _Econstructs were included at a fivefold excess. Fibrinogen was immunoprecipitated, from cell lysates (A) and culture medium (B), with antifibrinogen and run under reducing conditions. The size of protein markers (lane 1) is displayed in kD in the left margin.