1.1.1.3 both catalytic domains of the enzyme, performing each one of the enzyme activities, are expressed separately with or without the interface region, resulting in increased activity of each domain compared to the wild-type bifunctional holoenzyme, the isolated catalytic domains are no longer allosterically regulated, expression of hybrid holoenzyme AKIII-HDHI+ 1.1.1.3 expression in Escherichia coli 1.1.1.3 gene akthr2, DNA sequence determination and analysis, located on chromosome 4, subcloning in Escherichia coli strain DH5alpha, functional complementation of the Saccharomyces cerevisiae homoserine dehydrogenase-deficient hom6 mutant strain and of the aspartate kinase-deficient hom3 mutant strain, conferring L-threonine and L-methionine prototrophy to the yeast cells 1.1.1.3 gene hom, DNA and amino acid sequence determination and analysis, expression in the auxotroph mutant Escherichia coli CGSC 5075 1.1.1.3 gene hom, recombinant expression of His-tagged enzyme in Echerichia coli strain Rosetta (DE3) pLysS 1.1.1.3 gene hom, recombinant expression of His-tagged wild-type and mutant enzymes in Echerichia coli strain Rosetta (DE3) pLysS 1.1.1.3 gene hom, recombinant overexpression in Escherichia coli strain BL21(DE3) 1.1.1.3 gene hom, recombinant overexpression of His-tagged enzyme in Escherichia coli strain Rosetta2 (DE3), expression of soluble enzyme at lower temperature of 25°C 1.1.1.3 gene hom1, recombinant expression of wild-type and mutant enzymes in Escherichia coli strain BL21(DE3), recombinant overexpression of constructs comprising the enzyme with homoserine kinase, aspartate kinase, acetohydroxy acid synthase, or threonine dehydratase, overview 1.1.1.3 gene HOM6, DNA and amino acid sequence determination and analysis from the strain SC5314 genome, sequence comparison, reintegration of the gene encoding the wild-type enzyme into HOM6-deletion strains 1.1.1.3 gene PH1075, recombinant expression of His-tagged wild-type and mutant enzymes in Escherichia coli strain BL21 (DE3) codon plus-RIPL 1.1.1.3 gene thrA, functional recombinant expression in Escherichia coli strain Rosetta (DE3) pLysS 1.1.1.3 gene thrA, recombinant overexpression of enzyme mutant G433R in Escherichia coli strain Bl21 1.1.1.3 gene TM_0547 , sequence comparisons, recombinant expression of the enzyme in Escherichia coli strain BL21(DE3) 1.1.1.3 introduction of the gene homFBR allele into strain HL1049 1.1.1.3 overexpression in Escherichia coli 1.1.1.3 overexpression of AK-HSDH isoform 1 in Escherichia coli 1.1.1.3 recombinant expression of the enzyme in Escherichia coli strain BL21(DE3) 1.1.1.3 recombinant expression of wild-type and mutant enzymes in Escherichia coli strain BL21