Table 1.
Natural LacI/GalR homologs
| Natural proteina | ‘X’ abbreviation | Allosteric response | Position numbersb | Effector ligand |
|---|---|---|---|---|
| LacI | – | Induction | 1–360 | Allolactose; IPTG (18,56) |
| PurR | P | Co-repression | 60–341 | Hypoxanthine; guanine (38,39) |
| GalR | G | Induction | 60–343 | Galactose; fucose (82) |
| GalS | S | Induction | 60–346 | Galactose; fucose (45) |
| FruR (CRA) | F | Induction | 62–334 | Fructose-1-phosphate (83,84) |
| TreR | T | Induction | 63–315 | Trehalose-6-phosphate (85) |
| RbsR | R | Induction | 60–330 | Ribose (86) |
| CytR | C | Induction | 57–330 | Cytidine (87) |
| CelRc | E | Induction | 65–340 | Cellobiose (88) |
| AscG | A | None known | 60–334 | Transcription occurs when IS186 is inserted into ascG (44,61) |
aLacI, Lactose repressor protein; PurR, Purine repressor protein; GalR, Galactose repressor protein; GalS, Galactose isorepressor protein; FruR, Fructose repressor protein, which is also called the ‘catabolite repressor/activator’ (CRA); TreR, Trehalose repressor protein; RbsR, Ribose repressor protein; CytR, Cytidine repressor protein; CelR, Cellobiose repressor protein; AscG, Cryptic asc operon repressor. bThe total numbers of amino acids are indicated for LacI. For chimeras, the numbers correspond to the amino acids of the parent regulatory domains that are fused to the LacI DNA-binding domain/linker (positions 1–62). cFrom Thermobifida fusca. All other proteins are from E. coli.