Wild-type LacI/GalR proteins used to create the LXhXa chimeras.

a: Nomenclature: “L” indicates the LacI DNA binding domain (positions 1–44), “Xh” represents the protein source of the linker (positions 45–61), and the final “X” indicates the source of the regulatory domain. LPhP57cs has a linker sequence comprising PurR 45–56 and LacI 57–61 [21]. LGhP comprises the LacI DNA binding domain, the GalR linker, and the PurR regulatory domain.b: All proteins are from E. coli. LacI: Lactose repressor protein. RbsR: Ribsose repressor. FruR: Fructose repressor. GalR: Galactose repressor. GalS: Galactose isorepressor. PurR: Purine repressor. TreR: Trehalose repressor. AscG: Cryptic asc operon repressor.c: Point mutations listed in this table were generated in earlier studies [17], [18]. For this study, LLhT/V52A and LLhA/Q55A were used to generate mutations at most other positions because, if mutations were carried out in the weak repressors LLhT and LLhA, subsequent functional changes might be undetectable (as occurred for many variants of LGhP). A second rationale for using chimeras with point mutations was to compare outcomes between polymorphic variants (for example LLhG and LLhG/E62K). In either case, the noted position was fixed while other linker positions are mutated. (For example, position 62 was not further mutated in LLhG/E62K.).d: These values were determined in the absence of allosteric effector for all inducible repressors and LLhA, which has no known inducer. For the co-repressible chimeras based on PurR, values are shown for the presence of effector.e Lacks the eleven C-terminal amino acids of the tetramerization domain [34].