Figure 1.

(A) FROGS. Protein from pools of 100 cDNA plasmids was synthesized in vitro by coupled transcription/translation. A gel mobility shift assay on radiolabeled P3 site was performed in the presence or absence of HA, a truncated mutant of Mix.1 that encodes just the homeodomain. Pools with a specific gel mobility shift were sib-selected to isolate pure clones. (B) Sib selection of a sample pool. The gel mobility shift is detected in the primary pool (pool 22). The activity becomes more prominent with sib selection to pools of 12 cDNA clones (22B) and finally with the pure cDNA clone (22B8) when homodimers are evident. The HA heterodimer is marked. Note: the unprogrammed lysate (labeled H₂O) contains no added plasmid and characteristically gives high background on gel mobility shift analysis.