Figure 2. Rescue of E. coli auxotrophs by de novo proteins.

(A) E. coli strain BW25113 Δfes was transformed with a control plasmid overexpressing LacZ (left half), or with a library of plasmids encoding the collection of novel proteins (right half). Cells were plated on M9-glucose supplemented with 50 µM IPTG, 30 µg ml⁻¹ kanamycin, and 34 µg ml^-1 chloramphenicol. Cells transformed with the control plasmid fail to grow, whereas cells transformed with the library yield occasional colonies. (B) Similar results for ΔilvA. (Similar results were also observed for ΔserB and ΔgltA – data not shown.) (C) Re-transformation of ΔilvA cells with a single sequence, syn-ilvA-1. A similar number of colonies grow on M9-glucose (left) as on LB (right). Results for other sequences were similar to those shown in (C), and are summarized in Figure S1.