FIG. 12.

Ancestry of regulatory proteins and the operators to which they bind. Acinetobacter PobR (9), Acinetobacter PcaU, Pseudomonas PcaR (52), and Erwinina KdgR (45) have a common ancestry and respond to chemically different effectors. E. coli GlpR (7) is a member of a different evolutionary family of regulatory proteins, but comparison of identical nucleotide residues (represented by shading) raises the possibility of a common ancestry for the glp operator and operators associated with aromatic catabolism in Acinetobacter and Pseudomonas. Arrows, inverted repetitions.