DNA coding for a protein which imparts L-homoserine resistance to Escherichia coli bacterium, and a method for producing L-amino acids

Abstract

A bacterium which has an ability to produce an amino acid and in which a novel rhtB gene encodes a protein having an activity of making a bacterium having the protein L-homoserine-resistant is enhanced, is cultivated in a culture medium to produce and cause accumulation of the amino acid in the medium, and the amino acid is recovered from the medium.

1 . A method for producing an amino acid selected from the group consisting of L-threonine, L-homoserine, L-alanine, L-isoleucine, and L-valine comprising: 
 A) cultivating a bacterium which has an ability to produce an amino acid in a medium, and    b) recovering said amino acid from the medium,    wherein said bacterium belongs to the genus  Escherichia , and wherein L-homoserine resistance of said bacterium is enhanced by amplifying a copy number of a DNA in said bacterium, wherein said DNA is able to hybridize under stringent conditions to nucleotides 557 to 1171 of SEQ ID NO: 1, wherein said DNA is not less than 70% homologous to nucleotides 557 to 1171 of SEQ ID NO: 1, and wherein said DNA encodes a protein which has an activity of imparting L-homoserine resistance to a bacterium having the protein.    
     
     
         2 . The method according to  claim 1 , wherein said amino acid is at least one selected from the group consisting of L-alanine, L-isoleucine, and L-valine.  
     
     
         3 . The method according to  claim 1 , wherein said DNA is carried on a multi-copy vector.  
     
     
         4 . The method according to  claim 1 , wherein said DNA is carried on a transposon.  
     
     
         5 . A method for producing an amino acid selected from the group consisting of L-threonine, L-homoserine, L-alanine, L-isoleucine, and L-valine comprising: 
 A) cultivating a  Escherichia  bacterium which has been transformed with a mutant DNA in a medium, wherein said  Escherichia  bacterium has an ability to produce the amino acid, and    B) recovering the amino acid from the medium,    wherein said mutant DNA is obtainable by mutating a DNA comprising nucleotides 557 to 1171 of SEQ ID NO: 1 and selecting a mutant DNA which, when transferred into a bacterium increases the homoserine resistance of the bacterium as compared to the bacterium prior to receiving said mutant DNA, and wherein said mutant DNA is not less than 70% homologous to nucleotides 557 to 1171 of SEQ ID NO:1.    
     
     
         6 . The method according to  claim 5 , wherein said amino acid is at least one selected from the group consisting of L-alanine, L-isoleucine, and L-valine.  
     
     
         7 . The method according to  claim 5 , wherein said DNA is carried on a multicopy vector.  
     
     
         8 . The method according to  claim 5 , wherein said DNA is carried on a transposon.  
     
     
         9 . The method according to  claim 5 , wherein said DNA is derived from a bacterium belonging to the genus  Escherichia.    
     
     
         10 . The method according to  claim 9 , wherein said amino acid is at least one selected from the group consisting of L-alanine, L-isoleucine, and L-valine.  
     
     
         11 . The method according to  claim 9 , wherein said DNA is carried on a multicopy vector.  
     
     
         12 . The method according to  claim 9 , wherein said DNA is carried on a transposon.  
     
     
         13 . A method for producing an amino acid selected from the group consisting of L-threonine, L-homoserine, L-alanine, L-isoleucine, and L-valine comprising: 
 A) cultivating a bacterium which has an ability to produce the amino acid in a medium, and    B) recovering the amino acid from the medium,    wherein said bacterium belongs to the genus  Escherichia , wherein L-homoserine resistance of said bacterium is enhanced by amplifying a copy number of a DNA in said bacterium, wherein said DNA is derived from a bacterium belonging to the genus  Escherichia , wherein said DNA is able to hybridize under stringent conditions to nucleotides 557 to 1171 of SEQ ID NO: 1, wherein said DNA is not less than 70% homologous to nucleotides 557 to 1171 of SEQ ID NO: 1, and wherein said DNA encodes a protein which has an activity of imparting L-homoserine resistance to a bacterium having the protein.    
     
     
         14 . The method according to  claim 13 , wherein said amino acid is at least one selected from the group consisting of L-alanine, L-isoleucine, and L-valine.  
     
     
         15 . The method according to  claim 13 , wherein said DNA is carried on a multicopy vector.  
     
     
         16 . The method according to  claim 13 , wherein said DNA is carried on a transposon.