Novel Gene and Method for Producing L-Amino Acids

Abstract

The present invention describes a bacterium which has an ability to produce an amino acid and in which the rhtC gene encoding a protein having an enhanced activity of imparting L-threonine resistance to a bacterium expressing the protein. Preferably, the bacterium further includes an rhtB gene encoding for a protein having an enhanced activity of imparting to a bacterium L-homoserine resistance expressing the protein. The present invention also describes a method of cultivating the bacterium in a culture medium to produce and accumulate amino acids in the medium, and the amino acid is recovered from the medium.

What is claimed is: 
     
         1 . A method for producing the amino acid L-hormoserine or L-threonine, comprising the steps of:
 i) cultivating a bacterium belonging to the genus  Escherichia , which has the ability to produce the amino acid, in a culture medium, to produce and accumulate the amino acid in the medium, and   ii) recovering the amino acid from the medium,   wherein L-threonine resistance of said bacterium is enhanced by increasing the activity of a protein in said bacterium, wherein the protein is selected from the group consisting of:   (A) a protein comprising the amino acid sequence shown in SEQ ID NO: 4; and   (B) a protein comprising the amino acid sequence shown in SEQ ID NO: 4, but which includes deletion, substitution, insertion or addition of one or several amino acids in the amino acid sequence, and which has the activity of conferring resistance to L-threonine to the bacterium,   wherein the protein is encoded by a DNA selected from the group consisting of:   (a) a DNA comprising the nucleotide sequence of nucleotide numbers 187 to 804 in SEQ ID NO: 3;   (b) a DNA which hybridizes with a nucleotide sequence of nucleotide numbers 187 to 804 in SEQ ID NO: 3 under stringent conditions, and which encodes a protein having the activity of conferring resistance to L-threonine to the bacterium, wherein the stringent conditions comprise washing at 60° C. and at a salt concentration corresponding to 1×SSC and 0.1% SDS.   
     
     
         2 . The method according to  claim 1 , wherein the L-homoserine resistance of said bacterium is enhanced by increasing the activity of a protein in the bacterium, wherein the protein is selected from the group consisting of:
 (C) a protein comprising the amino acid sequence shown in SEQ ID NO: 2; and   (D) a protein comprising the amino acid sequence of SEQ ID NO: 2, but which includes deletion, substitution, insertion or addition of one or several amino acids in the amino acid sequence shown in SEQ ID NO: 2, and which has the activity of making a bacterium having the protein L-homoserine-resistant.   
     
     
         3 . The method according to  claim 2 , wherein the protein as defined in (C) or (D) is encoded by a DNA selected from the group consisting of:
 (c) a DNA comprising the nucleotide sequence of nucleotide numbers 557 to 1171 in SEQ ID NO: 1;   (d) a DNA which hybridizes with a nucleotide sequence of nucleotide numbers 557 to 1171 in SEQ ID NO: 1 under stringent conditions and which encodes a protein having the activity of conferring resistance to L-homoserine to the bacterium, wherein the stringent conditions comprise washing at 60° C., and at a salt concentration corresponding to 1×SSC and 0.1% SDS.   
     
     
         4 . A method for producing an amino acid, comprising the steps of:
 i) cultivating a bacterium belonging to the genus  Escherichia , which has the ability to produce the amino acid, in a culture medium, to produce and accumulate the amino add in the medium, and   ii) recovering the amino acid from the medium,   wherein L-threonine resistance of said bacterium is enhanced by increasing the activity of a protein in the bacterium, wherein the protein is selected from the group consisting of:   (A) a protein comprising the amino acid sequence shown in SEQ ID NO: 4; and   (B) a protein which comprises the amino acid sequence including deletion, substitution, insertion or addition of one or several amino acids in the amino acid sequence shown in SEQ ID NO: 4, and which has the activity of conferring resistance to L-threonine to bacterium,   wherein the protein is encoded by a DNA selected from the group consisting of:   (a) a DNA comprising the nucleotide sequence of nucleotide numbers 187 to 804 in SEQ ID NO: 3;   (b) a DNA which hybridizes with a nucleotide sequence of nucleotide numbers 187 to 804 in SEQ ID NO: 3 under stringent conditions and which encodes a protein having the activity of conferring resistance to L-threonine to the bacterium, wherein the stringent conditions comprise washing at 60° C. and at a salt concentration corresponding to 1×SSC and 0.1% SDS,   and wherein the L-homoserine resistance of said bacterium is enhanced by increasing the activity of a protein in the bacterium, wherein said protein is selected from the group consisting of:   (C) a protein comprising the amino acid sequence shown in SEQ ID NO: 2; and   (D) a protein comprising the amino acid sequence of SEQ ID NO: 2, but which includes deletion, substitution, insertion or addition of one or several amino acids in the amino acid sequence shown in SEQ ID NO: 2, and which has the activity of conferring resistance to L-homoserine to the bacterium.   
     
     
         5 . The method according to  claim 4 , wherein said amino acid is branched chain amino acid. 
     
     
         6 . The method according to  claim 5 , wherein said branched chain amino acid is L-valine or L-leucine. 
     
     
         7 . The method according to  claim 4 , wherein the protein as defined in (C) or (D) is encoded by a DNA selected from the group consisting of:
 (c) a DNA comprising the nucleotide sequence of nucleotide numbers 557 to 1171 in SEQ ID NO: 1;   (d) a DNA which hybridizes with a nucleotide sequence of nucleotide numbers 557 to 1171 in SEQ ID NO: 1 under stringent conditions and which encodes a protein having the activity of conferring resistance to L-homoserine to the bacterium, wherein the stringent conditions comprise washing at 60° C., and at a salt concentration corresponding to 1×SSC and 0.1% SDS.