Abstract: A method is provided for obtaining an L-amino acid or nucleic acid-producing bacterium belonging to the genus Escherichia with an optimized level of expression of the gene which influences the distribution of carbon flow, such as the sucAB genes, comprising introducing into the chromosome of the bacterium a set of in vitro constructed DNA fragments which contain regulatory elements for gene expression instead of the native elements of the regulatory region of the gene, and selecting the colonies with increased L-amino acid productivity. Also, a method is provided for producing an L-amino acid, such as L-glutamic acid, L-proline, L-arginine, L-glutamine, L-leucine, using the bacterium with an optimized level of expression of the sucAB gene.

Abstract: The present invention relates to a method for producing L-amino acids, such as L-tryptophan, L-phenylalanine, and L-tyrosine, using a bacterium belonging to the genus Escherichia, and wherein the L-amino acid productivity of said bacterium is enhanced by enhancing a PEP carboxykinase activity, which is coded by the pckA gene.

Abstract: A Mob? plasmid having a RSF1010 replicon, comprising a gene coding for Rep protein and said plasmid has been modified to inactivate gene related to mobilization ability. The present invention also describes a bacterium having an ability to produce useful metabolites, comprising the plasmid and said bacterium lack active thymidylate synthase coded by thyA gene and thymidine kinase coded by tdk gene, and a method for producing useful metabolites, such as native or recombinant proteins, enzymes, L-amino acids, nucleosides and nucleotides, vitamins, using the bacterium.

Abstract: A method for producing L-amino acids, such as L-tryptophan, L-phenylalanine, and L-tyrosine, using a bacterium of the Enterobacteriaceae family is provided. The L-amino acid productivity of said bacterium is increased by enhancing an activity of 6-phosphogluconolactonase, which is encoded by the pgl gene (ybhE ORF).