Fig. 2. The preduplication ancestral gene complements both paralogs.

(A) Growth of ancestral MADS-box gene strains using ornithine as a sole nitrogen source. Ornithine is converted into arginine and then modified to produce the other essential amino acids. In the absence of a functional ARG gene regulatory complex, strains cannot use ornithine as a nitrogen source. The preduplication AncMADS can supply the function of the modern Arg80 paralog (purple), but the postduplication AncMcm1 paralog cannot (blue). “Growth” on the y axis is the ratio of optical density at 600 nm (OD₆₀₀) at the indicated time point divided by OD₆₀₀ at time zero. (B to E) Gene expression profiling of ancestral MADS-box proteins in S. cerevisiae quantified with NanoString (www.nanostring.com). (B) MADS-box activated ARG genes. Row 1, CAR1; row 2, CAR2. (C) MADS-box repressed ARG genes. Row 1, ARG3; row 2, ARG5,6. (D) MADS-box activated mating genes (α-specific genes). Row 1, SAG1; row 2, MFa1; row 3, STE3. (E) MADS-box repressed mating genes (a-specific genes). Row 1, STE2; row 2, STE6. In each experiment, mean and standard error (indicated by error bars) were determined using three replicates.