Table 1. Multicopy Suppressors Rescue 21 Conditional Auxotrophs, via 8 Proposed Mechanisms.
| Strain | Protein Deficiency | MS | Rescuing Gene Product |
|---|---|---|---|
| Isozyme overexpression | |||
| ΔglyA | Glycine hydroxymethyltransferase | ltaE | l-allo-threonine aldolase |
| ΔilvA | Threonine dehydratase (biosynthetic) | tdcB | Threonine dehydratase (catabolic) |
| ΔilvE | Branched-chain amino acid transferase | avtA | Valine-pyruvate AT |
| ΔmetC | Cystathionine β-lyase/cysteine desulfhydrase | malY | Cystathionine β-lyase/maltose regulon repressor |
| Substrate ambiguity | |||
| ΔglnA | Glutamine synthetase | asnB | Asparagine synthetase |
| ΔpdxB | Erythronate-4-phosphate dehydrogenase | tdh | Threonine dehydrogenase |
| ΔserB | Phosphoserine phosphatase | gph | Phosphoglycolate phosphatase |
| ΔserB | Phosphoserine phosphatase | hisB | IGP dehydratase/histidinol phosphate phosphatase |
| ΔserB | Phosphoserine phosphatase | ytjC | Predicted bisphosphatase; uncharacterized |
| Ambiguity in metabolite transport | |||
| Δfes | Enterochelin esterase | setB | Predicted lactose/IPTG efflux transporter |
| ΔilvA | Threonine dehydratase (biosynthetic) | emrD | Multidrug efflux transporter |
| Δppc | Phosphoenolpyruvate carboxylase | ecfM | Predicted extracytoplasmic factor; uncharacterized |
| Δppc | Phosphoenolpyruvate carboxylase | yccT | Predicted outer membrane protein; uncharacterized |
| ΔptsI | Carbohydrate PTS system, enzyme I | fucP | Fucose transporter |
| ΔptsI | Carbohydrate PTS system, enzyme I | xylE | Xylose transporter |
| Catalytic promiscuity | |||
| Δfes | Enterochelin esterase | thiL | Thiamine monophosphate kinase |
| ΔmetC | Cystathionine β-lyase/cysteine desulfhydrase | alr | Alanine racemase |
| ΔpabA | Aminodeoxychorismate synthase, small subunit | menF | Isochorismate synthase |
| ΔpabB | Aminodeoxychorismate synthase, large subunit | menF | Isochorismate synthase |
| ΔpdxB | Erythronate-4-phosphate dehydrogenase | purF | Glutamine PRPP amidotransferase |
| ΔpurK | Carboxyaminoimidazole ribonucleotide synthetase | anmK | Anhydro-N-acetylmuramic acid kinase |
| Maintaining metabolic flux | |||
| ΔilvD | Dihydroxy-acid dehydratase | avtA | Valine-pyruvate AT |
| ΔpurK | Carboxyaminoimidazole ribonucleotide synthetase | purE | Carboxyaminoimidazole ribonucleotide mutase |
| Metabolic pathway bypass and/or alternate source of downstream substrate | |||
| ΔcarA | Carbamoyl phosphate synthase, small subunit | carB | Carbamoyl phosphate synthase, large subunit |
| ΔglyA | Glycine hydroxymethyltransferase | tdh | Threonine dehydrogenase |
| ΔglyA | Glycine hydroxymethyltransferase | yneH | Predicted glutaminase; uncharacterized |
| ΔhisH | IGP synthase; small subunit | hisF | IGP synthase; large subunit |
| ΔpabA | Aminodeoxychorismate synthase, small subunit | pabB | Aminodeoxychorismate synthase, large subunit |
| ΔptsI | Carbohydrate PTS system, enzyme I | galE | UDP-glucose 4-epimerase |
| ΔserA | Phosphoglycerate dehydrogenase | yneH | Predicted glutaminase; uncharacterized |
| ΔserC | Phosphoserine AT/phosphohydroxythreonine AT | yneH | Predicted glutaminase; uncharacterized |
| Regulatory effects | |||
| ΔcarA | Carbamoyl phosphate synthase, small subunit | ygiT | Predicted transcriptional regulator; uncharacterized |
| ΔglyA | Glycine hydroxymethyltransferase | rsd | Anti-sigma factor |
| ΔmetC | Cystathionine β-lyase/cysteine desulfhydrase | fimE | Recombinase for fimbrial phase switching |
| ΔmetR | Transcriptional activator of methionine biosynthesis | metE | Homocysteine transmethylase |
| ΔpurK | Carboxyaminoimidazole ribonucleotide synthetase | cpdA | Cyclic adenosine monophosphate phosphodiesterase |
| Unknown | |||
| ΔcarA | Carbamoyl phosphate synthase, small subunit | cho | Stress (SOS)-induced endonuclease for DNA repair |
| ΔcarA | Carbamoyl phosphate synthase, small subunit | yncK | Predicted transposase; uncharacterized |
| ΔpurF | Glutamine PRPP amidotransferase | chbA | Carbohydrate phosphotransferase system, enzyme IIChb |
| ΔyhhK | Putative acetyltransferase | murI | Glutamate racemase |
| ΔyhhK | Putative acetyltransferase | purF | Glutamine PRPP amidotransferase |
Note.-MS, multicopy suppressor; AT, aminotransferase; IGP, imidazole glycerol phosphate; PRPP, phosphoribosylpyrophosphate; UDP, uridine diphosphate.